JPWO2005062434A1 - Surface emitting laser and laser projection apparatus - Google Patents

Abstract

The present invention provides a surface emitting light having an active layer (3) formed on a semiconductor substrate (2a), and a pair of upper electrode (5) and lower electrode (6) for injecting carriers into the active layer (3). In the laser (100a), the planar shape of the lower electrode (6) is such that current injection from the lower electrode (6) to the active layer (3) is high in the central portion of the lower electrode (6). In the surrounding area, a star shape is formed so as to be performed at a low current density. In this surface-emitting laser (100a), the density distribution of carriers injected into the active layer of the surface-emitting laser becomes a distribution according to the light power distribution in the active layer. The occurrence of hole burning due to the increase in current density in the corresponding region can be avoided, and the lateral mode stability at the time of high output can be greatly increased to improve the high output characteristics.

Description

  The present invention relates to a surface emitting laser and a laser projection device, and more particularly to a surface emitting laser that operates stably at a high output and a laser projection device using the surface emitting laser as a light source.

  Surface-emitting lasers are semiconductor lasers that perform laser oscillation at a low threshold and have excellent beam quality, and can be applied to the optical communication field using modulation characteristics that output light can be modulated at high speed. ing. However, there is a problem that it is difficult to increase the output as a problem of the surface emitting laser.

  Since the surface emitting laser is composed of a thin film, the resonator length is very short due to its structure. For this reason, it is difficult to increase the resonator length to obtain a sufficient gain.

  On the other hand, it is conceivable to increase the driving current of the surface emitting laser to increase the output, but in the surface emitting laser, when the carrier density in the active layer is too high, the light output is increased due to gain saturation due to spatial hole burning. Saturation impedes high light output operation.

  For this reason, it is effective to increase the beam cross-sectional area of the surface-emitting laser in order to increase the output of the surface-emitting laser without increasing the resonator length or driving current. Conceivable.

  However, in such a surface emitting laser with a short resonator length, if the beam cross-sectional area is increased in order to increase the output of the laser, the transverse mode in the resonator becomes multimode, and the beam quality is increased. In addition, there has been a problem that the oscillation efficiency is remarkably lowered.

  On the other hand, surface emitting lasers that have eliminated such beam quality and oscillation efficiency degradation have already been developed. For example, Patent Document 1 discloses that the surface emitting lasers have multiple transverse modes. An increase in beam cross-sectional area while suppressing is disclosed.

  14A and 14B are diagrams for explaining the surface emitting laser disclosed in Patent Document 1. FIG. 14A shows the cross-sectional structure, FIG. 14B shows the shape of the lower electrode, and FIG. (C) shows the light intensity distribution in the region facing the lower electrode of the active layer of this surface emitting laser.

  A surface emitting laser 200 shown in FIG. 14A has a semiconductor substrate 2, an active layer 3 formed on one surface of the semiconductor substrate 2, and a reflective layer 4 formed on the active layer 3. is doing. Here, the reflective layer 4 is a dispersive black reflective layer formed by alternately laminating materials 4a and 4b having different refractive indexes, and is hereinafter also referred to as a DBR (Distributed Bragg Reflector) layer. The surface emitting laser 200 is formed so as to surround a circular lower electrode 600 formed on the surface of the DBR layer 4 and a region facing the lower electrode 600 on the other surface of the substrate 2. And an upper electrode 5 having a ring shape.

The surface-emitting laser 200 has an external mirror 1 disposed above the surface electrode 5 so as to face the inner substrate surface. In the surface-emitting laser 200, the DBR layer 4 and an external The mirror 1 constitutes a resonator that amplifies the light generated in the active layer 3 so that laser oscillation occurs. Here, the DBR layer 4 is a total reflection layer, and the external mirror 1 is a partially transmissive mirror.
Next, the operation will be described.

  In the surface emitting laser 200, when a driving voltage is applied between the upper electrode 5 and the lower electrode 600 and a current is injected into the active layer 3, light is generated in the active layer 3, and the generated light is resonant. Amplified by the instrument. When the magnitude of the injection current becomes a certain value, that is, larger than the laser oscillation threshold, laser oscillation occurs in the resonator, and the laser beam 8 is emitted to the outside via the external mirror 1. At this time, the laser light 8 is surface-emitted, and the emission direction of the laser light is a direction perpendicular to the surface of the substrate 2.

  As described above, in the surface emitting laser disclosed in Patent Document 1, one of the mirrors constituting the resonator is arranged as an external mirror 1 apart from the substrate to increase the resonator length. That is, by using such an external mirror 1, even if the beam cross-sectional area has a large value, the resonance mode can be made single, and high output characteristics are realized.

  Patent Document 2 discloses an electrode structure for making the carrier density in the active layer uniform in a surface emitting laser.

In the surface emitting laser disclosed in Patent Document 2, the distribution of the current injected into the active layer can be controlled by dividing the back electrode into a plurality of parts, thereby realizing a large surface emitting laser. Yes.
US Pat. No. 6,404,797 Japanese Patent Laid-Open No. 11-233889

  However, in the surface emitting laser 200 disclosed in Patent Document 1, the carrier density distribution in the active layer becomes a problem when realizing high output characteristics. That is, in the surface emitting laser 200 described in this document, the light intensity distribution in the region corresponding to the lower electrode 600 of the active layer 3 is a distribution close to a Gaussian distribution as shown in FIG. The light intensity Lp has a peak at the light emission center portion of the layer. On the other hand, in the region corresponding to the lower electrode 600 in the active layer 3 of the surface emitting laser 200, the light is not injected into the active layer 3 even though there is a large deviation in the light intensity distribution between the central portion and the peripheral portion. The carrier density Cd is uniform. For this reason, the density of carriers existing in the active layer is large in the peripheral portion of the central portion of the region corresponding to the lower electrode 600 of the active layer 3, and the carrier is in an excessive state. In the part, there is a shortage of carriers. Due to such a non-uniform distribution of carriers, a refractive index distribution is generated in the active layer 3 and the resonance mode becomes multi-dimensional. Furthermore, there is a concern about the occurrence of gain saturation.

This phenomenon is caused by an infrared semiconductor laser made of an AlGaAs-based semiconductor material (Al _x Ga _1-x As (0 ≦ x ≦ 1)) or an AlGaInP-based semiconductor material (Al _x Ga _y In _1-xy P (0 Compared with a red semiconductor laser having a relation of ≦ x ≦ 1, 0 ≦ y ≦ 1)), this is particularly remarkable in a nitride semiconductor laser having a very high threshold carrier density and high differential gain.

  In addition, the surface emitting laser disclosed in Patent Document 2 has a problem in that efficiency is lowered due to a loss in current injected into the active layer due to a portion of the resistance separation layer that divides a plurality of electrodes.

  The present invention solves the conventional problems as described above, and can perform laser oscillation in a stable transverse mode, and can efficiently inject current into an active layer. It is an object of the present invention to provide a light emitting laser and a laser projection apparatus using such a high output surface emitting laser as a light source.

  In order to solve the above-described problem, a surface emitting laser according to claim 1 of the present invention is a surface emitting laser that performs surface emission of laser light, and includes an active layer formed on a semiconductor substrate, and the active layer. A pair of electrodes for injecting carriers, and one of the pair of electrodes is composed of one electrode layer, and current injection from the one electrode to the active layer is performed at the center of the one electrode. This is performed at different current densities in the portion and the peripheral portion.

  As a result, the density distribution of carriers injected into the active layer can be adjusted in accordance with the light intensity distribution in the active layer, and the carrier distribution in the active layer can be made uniform. It is possible to realize a surface emitting laser having excellent high output characteristics, in which lateral mode stability during output is greatly increased.

  A surface-emitting laser according to a second aspect of the present invention is the surface-emitting laser according to the first aspect, wherein the surface-emitting laser includes a semiconductor layer stack including the active layer formed by stacking a plurality of semiconductor layers on the semiconductor substrate. The surface density at which the electrode layer and the semiconductor layer laminate are in contact with each other is different between the central portion of the electrode layer and the peripheral portion thereof.

  As a result, the density distribution of carriers injected into the active layer can be adjusted by the contact area between the electrode layer and the semiconductor layer stack, and the carrier distribution in the active layer having a light intensity distribution can be made uniform. Can be realized by a simple method such as changing the shape of the electrode layer.

  A surface-emitting laser according to a third aspect of the present invention is the surface-emitting laser according to the first aspect, wherein the one electrode has a plurality of micro holes in an electrode layer constituting the one electrode, and the occupation density of the micro holes is The center portion of the one electrode and the peripheral portion thereof are formed differently.

  Accordingly, the density distribution of carriers injected into the active layer can be adjusted by changing the arrangement of the micro holes formed in the electrode layer and the size of the micro holes, and the active layer having a light intensity distribution. Uniform carrier distribution can be realized by simple modification of the structure of the electrode layer. In addition, the spread of the entire electrode layer on the semiconductor layer can be increased to further enhance the heat dissipation effect from the electrode layer to the heat sink, and a surface emitting laser having more excellent high output characteristics can be realized.

  A surface-emitting laser according to a fourth aspect of the present invention is the surface-emitting laser according to the first aspect, wherein the one electrode has a resistance value of an electrode layer constituting the one electrode and a central portion of the one electrode and its periphery. It is characterized by being different from the part.

  As a result, the density distribution of carriers injected into the active layer can be adjusted more precisely according to the light intensity distribution in the active layer by changing the electrode layer material and components to change the resistance value of the electrode layer. be able to.

  The surface-emitting laser according to claim 5 of the present invention is the surface-emitting laser according to claim 1, wherein a semiconductor layer stack including the active layer, which is formed by stacking a plurality of semiconductor layers on the semiconductor substrate, A resistance layer formed between the semiconductor layer stack and an electrode layer constituting the one electrode, and a resistance value of the resistance layer is a portion corresponding to a central portion of the one electrode; It differs in the part corresponding to the peripheral part, It is characterized by the above-mentioned.

  Thereby, the density distribution of carriers injected into the active layer can be adjusted more precisely according to the light intensity distribution in the active layer by changing the material and components of the resistance layer.

  A surface-emitting laser according to a sixth aspect of the present invention is the surface-emitting laser according to the first aspect, wherein the surface-emitting laser includes a semiconductor layer stack including the active layer formed by stacking a plurality of semiconductor layers on the semiconductor substrate. And a resonator for amplifying the light generated in the active layer so as to cause laser oscillation, and the reflective layer included in the semiconductor layer stack and the semiconductor layer stack so as to face the reflective layer It is characterized by comprising an external mirror.

  As a result, the cavity length of the surface emitting laser can be increased, the cross-sectional area of the surface emitting laser can be increased while suppressing the transverse mode in the resonator from becoming multimode, and the high output characteristics of the surface emitting laser. Can be dramatically improved.

  The surface-emitting laser according to claim 7 of the present invention is the surface-emitting laser according to claim 6, wherein the external mirror is a partially transmissive mirror having concave surfaces on both sides. is there.

  This increases the divergence angle of the surface emitting laser light from the surface emitting laser, and a general-purpose lens with a large aperture and a short focal length can be used for the optical system that couples the surface emitting laser to an optical fiber or the like. Thus, the optical system can be made compact with a low cost and a short optical path length.

  The surface-emitting laser according to claim 8 of the present invention is the surface-emitting laser according to claim 1, wherein the surface-emitting laser has a semiconductor layer stack including the active layer formed by stacking a plurality of semiconductor layers on the semiconductor substrate. The semiconductor layer stack includes a supersaturated absorber that is disposed in the vicinity of the active layer and absorbs supersaturated carriers in the active layer.

  As a result, the oscillation state of the surface emitting laser is changed to a self-excited oscillation state utilizing a phenomenon of absorbing supersaturated carriers, that is, an oscillation state in which laser light is emitted in a pulsed manner even though a direct current is flowing. Speckle noise can be reduced.

  The surface-emitting laser according to claim 9 of the present invention is the surface-emitting laser according to claim 1, wherein the oscillation wavelength of the surface-emitting laser light is a wavelength within a range of 430 to 455 nm. Is.

  Thereby, it is possible to obtain a blue surface emitting laser that realizes low power consumption by reducing required power and high color reproducibility.

The surface-emitting laser according to claim 10 of the present invention is the surface-emitting laser according to claim 1, wherein the oscillation wavelength of the surface-emitting laser light is a wavelength in the range of 630 to 650 nm. Is.
Thereby, a red surface emitting laser realizing high output can be obtained.

A surface-emitting laser according to an eleventh aspect of the present invention is the surface-emitting laser according to the first aspect, wherein the oscillation wavelength of the surface-emitting laser light is a wavelength within a range of 510 to 550 nm. Is.
Thereby, a green surface emitting laser with high reliability can be realized.

A surface-emitting laser according to a twelfth aspect of the present invention is the surface-emitting laser according to the sixth aspect, wherein a non-linear optical material that converts the wavelength of the laser light disposed between the external mirror and the active layer is used. It is characterized by having.
As a result, a high-power laser light source that can generate short-wavelength light can be realized.

  The surface-emitting laser according to claim 13 of the present invention is the surface-emitting laser according to claim 1, wherein the semiconductor layer stack includes the active layer formed by stacking a plurality of semiconductor layers on the surface of the semiconductor substrate. The semiconductor substrate is formed by etching a part of the back surface to the vicinity of the surface of the active layer to form a recess.

  As a result, the absorption of laser light in the semiconductor substrate can be reduced, and high output can be achieved.

  According to a fourteenth aspect of the present invention, there is provided a semiconductor laser device comprising: a semiconductor laser that outputs a laser beam; and a wavelength conversion element that converts the wavelength of the laser beam from the semiconductor laser. Is a surface emitting laser according to claim 1.

  As a result, it is possible to realize a high-power semiconductor laser device capable of generating short-wavelength light, in which laser light from the surface-emitting laser is wavelength-converted and output.

  A laser module according to claim 15 of the present invention is a laser module in which a plurality of semiconductor lasers are integrated in one package, and each of the semiconductor lasers is a surface emitting laser according to claim 1. It is characterized by.

  Thereby, a multi-wavelength light source such as an RGB light source can be realized, and an ultra-compact laser irradiation apparatus can be realized by using such a multi-wavelength light source and a condensing optical system.

  The laser module according to a sixteenth aspect of the present invention is the laser module according to the fifteenth aspect, wherein each of the plurality of semiconductor lasers is positioned at a vertex of a regular polygon whose center coincides with the center of the package. It is arrange | positioned so that it may carry out.

  As a result, the package structure can be simplified and the cost can be reduced, and the output and life of the laser module can be increased.

  A laser projection apparatus according to claim 17 of the present invention is a laser projection apparatus comprising: a semiconductor laser that outputs laser light; and a projection optical system that projects the laser light output from the semiconductor laser. The laser is a surface emitting laser according to claim 1.

  As a result, it is possible to realize an ultra-compact laser projection device capable of achieving high output, in which the lateral mode stability at high output is greatly increased.

  The laser projection device according to an eighteenth aspect of the present invention is the laser projection device according to the seventeenth aspect, wherein the surface emitting laser emits a laser beam having a longitudinal mode spectrum of multimode. is there.

  Thereby, the coherency of the laser light is reduced, and speckle noise can be reduced.

  According to a nineteenth aspect of the present invention, there is provided the laser projection device according to the seventeenth aspect, wherein the surface emitting laser emits a laser beam having a substantial width of a longitudinal mode spectrum of 1 nm or more. It is a feature.

  Thereby, it is possible to realize a laser projection apparatus in which speckle noise is greatly reduced.

  A surface-emitting laser according to claim 20 of the present invention is a surface-emitting laser that performs surface emission of a laser beam, an active layer formed on a semiconductor substrate, and a pair of electrodes that inject carriers into the active layer; One of the pair of electrodes is divided into a plurality of electrode portions, and a laser drive voltage on which a high frequency component is superimposed is applied to at least one of the plurality of electrode portions. It is what.

  This makes it possible to adjust the density of carriers injected from each electrode portion into the active layer by the drive voltage applied to each electrode portion, and the active voltage can be obtained regardless of the light intensity distribution in the surface emitting laser active layer. It is possible to realize a surface emitting laser having excellent high output characteristics in which the carrier density in the layer is made uniform and the transverse mode stability at high output is greatly increased. In addition, since a laser drive voltage with a high frequency component superimposed on the electrode is applied, the laser oscillation state changes and the temporal coherency of the laser light is reduced, thereby reducing noise caused by the return light. Can do.

  The surface-emitting laser according to claim 21 of the present invention is the surface-emitting laser according to claim 20, wherein the plurality of divided electrode portions are arranged substantially uniformly around the emission center of the laser beam. It is characterized by that.

  Thus, by applying the same level of driving voltage to the electrode portions having the same distance from the emission center, it is possible to easily make the carrier density uniform in the active layers having different light intensity distributions.

  The surface emitting laser according to claim 22 of the present invention is the surface emitting laser according to claim 20, wherein the current density from the electrode portions to the active layer is closer to the emission center of the active layer. It is characterized in that it is performed so as to be higher.

  Thereby, the density distribution of the injected carrier suitable for the light intensity distribution can be realized in the active layer having the light intensity distribution in which the peak of the light intensity is located at the emission center.

  The surface emitting laser according to claim 23 of the present invention is the surface emitting laser according to claim 20, wherein a modulated laser driving voltage is applied to at least one of the plurality of electrode portions. It is.

  As a result, speckle noise can be suppressed by reducing coherency while alleviating the chirping phenomenon in which the oscillation wavelength varies.

  A surface-emitting laser according to a twenty-fourth aspect of the present invention is the surface-emitting laser according to the twentieth aspect, wherein each semiconductor laser portion formed by each electrode portion is driven with a different injection current. is there.

  As a result, in the active layer corresponding to each semiconductor laser, it becomes possible to realize a carrier injection density corresponding to the light intensity distribution, and to increase the output of the surface emitting laser while suppressing spatial hole burning. it can.

  The surface-emitting laser according to claim 25 of the present invention is the surface-emitting laser according to claim 20, wherein the semiconductor layer stack includes the active layer and is formed by stacking a plurality of semiconductor layers on the surface of the semiconductor substrate. The semiconductor substrate is formed by etching a part of the back surface to the vicinity of the surface of the active layer to form a recess.

  As a result, the absorption of laser light in the semiconductor substrate can be reduced, and high output can be achieved.

  According to the present invention, in the surface-emitting laser, the density distribution of carriers injected into the active layer of the surface-emitting laser is made to be a distribution according to the light power distribution in the active layer. It is possible to avoid the occurrence of hole burning due to an increase in current density in the region corresponding to the portion, and to greatly increase the transverse mode stability at the time of high output, thereby improving the high output characteristics.

  As a result, a high-power surface-emitting laser capable of performing laser oscillation in a stable transverse mode and efficiently injecting current into the active layer, and such a high-power surface-emitting laser as a light source. The laser projection apparatus used can be obtained.

FIG. 1 is a diagram for explaining a surface emitting laser according to Embodiment 1 of the present invention. In the cross-sectional structure (FIG. (A)), the shape of a lower electrode (FIG. (B)), and the light emitting region of an active layer. 2 shows the light intensity distribution (FIG. 2C). FIG. 2 is a diagram showing another example of the shape of the lower electrode in the surface emitting laser of the first embodiment (FIGS. (A) and (b)). FIG. 3 is a view showing another example (FIGS. (A) and (b)) of the lower electrode structure in the surface emitting laser according to the first embodiment. FIG. 4 is a diagram for explaining a surface emitting laser according to the second embodiment of the present invention. In the sectional structure (FIG. (A)), the shape of the lower electrode (FIG. (B)), and the light emitting region of the active layer. 2 shows the light intensity distribution (FIG. 2C). FIG. 5 is a plan view (FIG. 5A) and a cross-sectional view (FIG. 5B) for explaining an application example of the surface emitting laser according to the second embodiment. FIG. 6 is a diagram for explaining a laser projection apparatus according to Embodiment 3 of the present invention. FIG. 7 is a view for explaining a surface emitting laser according to Embodiment 4 of the present invention. FIG. 8 is a side view (FIG. (A)) and a plan view (FIG. (B)) for explaining an example of a laser module according to Embodiment 5 of the present invention. FIG. 9 is a side view (FIG. (A)) and a plan view (FIG. (B)) for explaining a modification of the surface emitting laser according to the fifth embodiment. FIG. 10 is a diagram for explaining a semiconductor laser device according to a sixth embodiment of the present invention. FIG. 11 is a diagram for explaining a modification of the semiconductor laser device according to the sixth embodiment. FIG. 12 is a diagram showing the relationship between the wavelength and output required for the laser projection apparatus according to the seventh embodiment of the present invention. FIG. 13 is a diagram for explaining the output wavelength of the laser projection apparatus of the seventh embodiment, and shows the relationship between the blue light source wavelength and the required output. FIG. 14 is a diagram showing an example of a conventional surface emitting laser.

Explanation of symbols

1, 10, 21 External mirror 2, 2a, 22 Semiconductor substrate 3, 23 Active layer 4, 24 DBR layer 5, 25 Upper electrode 6, 6a, 6b, 26, 60, 600 Lower electrode 7a, 7b, 7c, 7d Fine Hole 8 Laser beam 9, 29 Recess 11 Insulating film 11a, 11b, 11c, 12a, 12b Hole 26a, 60a Inner electrode part 26b, 60b Outer electrode part 61 Resistance separating part 62 Insulating separating layer 62a Separating layer 100a, 100b, 100d, 200 Surface emitting laser 101, 106 Red surface emitting laser 101a, 102a, 103a, 104a, 105a, 106a, 107a Lead terminal 102, 104, 105 Green surface emitting laser 103, 107 Blue surface emitting laser 110 Semiconductor layer stack 120, 160 , 160a Semiconductor laser device 130, 170 Laser projection device 132 lens 133 spatial modulator 134 a projection lens 135,173 screen 150,150a laser module 151 based member 161,161a wavelength converting element 172 projection optical system

  Embodiments according to the present invention will be described below in detail with reference to the drawings.

(Embodiment 1)
1A and 1B are diagrams for explaining a surface emitting laser according to Embodiment 1 of the present invention. FIG. 1A shows a sectional structure thereof, FIG. 1B shows a shape of a lower electrode thereof, and FIG. c) shows the light intensity distribution in the light emitting region of the active layer. In FIG. 1, the same reference numerals as those in FIG. 14 are the same as those in the conventional surface emitting laser.

  The surface emitting laser 100a according to the first embodiment is formed in a semiconductor layer stack 110 in which an active layer 3 and a reflective layer 4 are stacked on the surface of a semiconductor substrate 2a, and in a predetermined region on the reflective layer 4. A lower electrode 6 and a planar ring-shaped upper electrode 5 formed on the back side of the semiconductor substrate 2a are provided.

  Here, the semiconductor substrate is made of a nitrogen compound mainly containing GaN, and the active layer 3 is made of a nitride semiconductor mainly containing GaN. The reflective layer 4 is a dispersive black reflective layer (hereinafter referred to as a DBR layer) formed by alternately laminating materials 4 a and 4 b having different refractive indexes on the active layer 3.

  In the surface emitting laser 100a according to the first embodiment, the lower electrode 6 has a star shape obtained by cutting out a regular octagonal region of an isosceles triangle having each side as a base. Therefore, the surface density of the portion where the lower electrode 6 and the DBR layer 4 are in contact is large at the central portion of the lower electrode 6 and is small at the peripheral portion of the lower electrode 6. Here, the lower electrode 6 is arranged so that the center thereof coincides with the center of the ring-shaped upper electrode 5, and the maximum width is larger than the inner diameter of the ring-shaped upper electrode 5, and the outer diameter is larger than the outer diameter. It is a small one. Further, a portion of the semiconductor substrate 2a exposed to the inside of the upper electrode 5 is etched to the vicinity of the surface of the active layer 3, and is thinner than the other portions.

  The surface-emitting laser 100a according to the first embodiment has an external mirror 1 disposed above the ring-shaped upper electrode 5, and an active layer is formed by the external mirror 1 and the DBR layer 4. 3 is configured to amplify the light generated in 3 so that laser oscillation occurs. Here, the substrate side surface of the external mirror 1 has a concave shape.

Next, the function and effect will be described.
First, the laser oscillation operation of the surface emitting laser 100a according to the first embodiment will be briefly described.

  In the surface emitting laser 100 a, when a laser driving voltage is applied between the upper electrode 5 and the lower electrode 6, a current is injected into the active layer 3. When the magnitude of the injection current becomes a certain value, that is, larger than the laser oscillation threshold, laser oscillation occurs in the resonator, and the laser beam 8 is emitted outside through the external mirror 1. At this time, the laser beam 8 is surface-emitted, and the emission direction of the laser beam is perpendicular to the surface of the semiconductor substrate 2a.

  Next, the characteristics of the surface emitting laser according to the first embodiment will be described in comparison with the conventional one.

  In the conventional surface emitting laser, the lower electrode has an electrode structure in which a circular conductor layer is formed on the DBR layer 4. For this reason, if the injection current is increased in order to obtain high power, the current density at the periphery of the electrode increases, and due to the occurrence of hole burning, the gain decreases or the transverse mode becomes unstable, An increase in injected current causes a decrease in output and unstable operation. On the other hand, in the vicinity of the center of the electrode, a shortage of injected carriers occurs due to an increase in light power density. As described above, in the conventional surface emitting laser, when the output is high, the transverse mode becomes multi-level and the mode becomes unstable, and it is difficult to realize a stable transverse mode.

  On the other hand, in the surface emitting laser 100a according to the first embodiment, the shape of the lower electrode 6 is a star shape shown in FIG. It becomes possible to approximate the light intensity distribution in the active layer.

  That is, as shown in FIG. 1C, the light intensity distribution in the active layer 3 has the highest light intensity Lp at the emission center and decreases toward the periphery, and the light intensity distribution is close to a Gaussian distribution. It has become. Therefore, by making the planar shape of the lower electrode 6 into the star shape shown in FIG. 1B, the surface density of the portion where the lower electrode 6 and the DBR layer 4 are in contact with each other is reduced from the center of the lower electrode to the periphery. Decreases over time. In other words, the density of current (carrier) injected from the lower electrode 6 into the active layer 3 is maximized at the central portion of the lower electrode 6 and decreases as it goes to the peripheral portion, as shown in FIG. It becomes. As a result, the density distribution of the current injected into the active layer 3 corresponds to the light intensity distribution in the active layer 3, and the lateral mode stability at high output is greatly improved. A surface emitting laser having output characteristics can be realized.

  Conventionally, a surface emitting laser that can adjust the distribution of injected carrier density as a structure in which an electrode is divided into a plurality of parts has already been proposed. However, when the electrode of the surface emitting laser is divided, there is a problem that the resistance separation layer located at the portion where the electrode is divided causes a loss in the current injected into the active layer and the efficiency is lowered. In addition, in such a plurality of divided electrodes, the injected carrier density distribution can be changed only discretely, so that the density distribution of the injected carrier and the light intensity distribution are not sufficiently matched. Furthermore, since a laser driving voltage is applied to the divided electrodes so that current is injected into the active layer from each electrode at a different current density, the laser driving circuit becomes complicated. There was a problem.

  On the other hand, in the surface emitting laser 100a of the first embodiment, the planar shape of the lower electrode 6 is such that the surface density of the portion where the lower electrode 6 and the DBR layer 4 are in contact is the central portion of the lower electrode 6. Since it is star-shaped so as to be large and small in the peripheral portion of the lower electrode 6, the injected carrier density distribution can be continuously changed. Further, in the conventional surface emitting laser, resistance separation for separating the electrodes is possible. Since no layer is required, there is little injection current loss and efficient laser oscillation is possible.

  As described above, the first embodiment has the active layer 3 formed on the semiconductor substrate 2a and the pair of upper electrode 5 and lower electrode 6 for injecting carriers into the active layer 3, and the lower electrode 6 The star shape is such that current injection from the lower electrode 6 to the active layer 3 is performed at a high current density in the central portion of the lower electrode 6 and at a low current density in the peripheral portion. Therefore, the density distribution of carriers injected into the active layer 3 of the surface emitting laser can be set to a distribution according to the light power distribution in the active layer. This prevents the occurrence of hole burning due to an increase in current density in the region of the active layer corresponding to the periphery of the electrode, resulting in excellent high output characteristics that greatly increased lateral mode stability at high output. A surface emitting laser having the same can be realized.

  In the first embodiment, the region of the semiconductor substrate 2a facing the lower electrode 6 is thinned by etching to the vicinity of the surface of the active layer 3, so that the region of the active layer 3 faces the lower electrode 6. It is possible to reduce the absorption of the laser light generated in the portion by the semiconductor substrate 2a, and it is possible to efficiently extract the laser light from the back side of the semiconductor substrate 2a.

  Further, in the structure in which the laser light is extracted from the back surface side of the semiconductor substrate 2a in this way, a metal electrode layer having high thermal conductivity can be formed on the surface of the DBR layer 4 on the active layer 3 at a position close to the active layer. it can. Further, the surface emitting laser is configured such that the metal electrode layer as described above is disposed in close contact with the heat sink, whereby the heat generated in the active layer 3 can be efficiently released to the outside. The temperature rise in the active layer 3 can be suppressed, and the output of the surface emitting laser can be further increased.

  Further, in the first embodiment, the resonator of the surface emitting laser 100a is configured by the DBR layer 4 formed on the semiconductor substrate 2a and the external mirror 1 disposed away from the semiconductor substrate 2a. A sufficient resonator length can be secured. Thereby, the stability of the transverse mode of the resonator can be increased, and the light intensity distribution in the active layer 3 near the lower electrode 6 can be increased.

  For example, the range of the light intensity distribution in the active layer is substantially proportional to the resonator length, and the resonator length can be increased 10 times or more by using the external mirror 1, thereby enabling an effective active layer. The area can be increased. As a result, the surface emitting laser can dramatically improve the high output characteristics, which increase in proportion to the effective active layer area.

  In addition, in a surface emitting laser having a resonator having an external active mirror and having a large effective active layer area, the problem of the consistency between the light intensity distribution and the injected carrier distribution in the active layer 3 becomes significant. In Embodiment 1, since the planar shape of the lower electrode 6 of the surface emitting laser is a star shape, the inconsistency problem between the carrier density distribution and the light intensity distribution in the external mirror type surface emitting laser is solved, and the surface emitting Lasers have greatly improved high power characteristics.

  Further, in the surface emitting laser of the first embodiment, a self-excited oscillation state using supersaturated absorption, that is, a laser beam is emitted in a pulsed form as an output even though a current applied to the semiconductor laser is a direct current. The speckle noise can be reduced by changing the oscillation wavelength according to the oscillation state.

  That is, in the surface emitting laser of the first embodiment, the planar shape of the lower electrode 6 is such that current injection from the lower electrode 6 to the active layer 3 is performed at a high current density in the central portion of the lower electrode 6. Since the peripheral portion is shaped so as to be performed at a low current density, by providing a saturable absorber in a portion corresponding to the periphery of the lower electrode 6 in the active layer so as to reduce the injection current density, In high-power surface emitting lasers, speckle noise can be reduced by self-excited oscillation using supersaturated absorption.

  In the first embodiment, the planar shape of the lower electrode 6 is such that the surface density of the portion where the lower electrode 6 and the DBR layer 4 are in contact is continuously from the central portion of the lower electrode 6 to the peripheral portion thereof. Although the star shape is changed so as to change, the structure of the lower electrode 6 is not limited to such a planar star shape.

For example, the lower electrode 6 may be formed with a plurality of fine holes so that the surface density of the portion where the lower electrode 6 is in contact with the DBR layer 4 is different between the central portion of the lower electrode 6 and its peripheral portion.
FIG. 2 is a diagram for explaining an example of the structure of the lower electrode in which such fine holes are formed.

  A lower electrode 6a shown in FIG. 2A is obtained by forming a plurality of fine holes in a single electrode layer constituting the electrode. In the lower electrode 6a, the diameter of the minute hole 7a formed in the center is smaller than the diameter of the minute hole 7c formed in the peripheral part. Further, the diameter of the fine hole 7b formed in the intermediate part between the center part and the peripheral part of the lower electrode 6a is smaller than the diameter of the fine hole 7a formed in the central part, and the diameter of the fine hole 7c formed in the peripheral part. Greater than.

  The lower electrode 6a in which a plurality of fine holes are formed in this manner is similar to the lower electrode 6 of the first embodiment, the closer the surface density of the portion where the lower electrode 6a and the DBR layer 4 are in contact is closer to the center. As a result, the density distribution of carriers injected into the active layer of the surface emitting laser can be made to be a distribution corresponding to the power distribution of light in the active layer.

  Further, the lower electrode 6b shown in FIG. 2 (b) is formed by forming a plurality of fine holes in a single electrode layer constituting the electrode, like the lower electrode 6a shown in FIG. 2 (a). In the lower electrode 6b, the arrangement density of the fine holes 7d increases as it is closer to the periphery.

  The lower electrode 6b in which a plurality of fine holes are formed in this manner is similar to the lower electrode 6 of the first embodiment, the closer the surface density of the portion where the lower electrode 6b and the DBR layer 4 are in contact is closer to the center thereof. As a result, the density distribution of carriers injected into the active layer of the surface emitting laser can be made to be a distribution corresponding to the power distribution of light in the active layer.

  In the lower electrode 6a shown in FIG. 2A or the lower electrode 6b shown in FIG. 2B, a metal layer constituting the lower electrode is easily formed by selective etching using a mask. Can do.

  In addition, the lower electrode having a plurality of such fine holes can be formed so as to spread over the entire region where the hole can be arranged, thereby improving the heat dissipation effect to the heat sink.

In the first embodiment, the density of the current injected into the active layer is adjusted to match the light intensity distribution in the active layer by the planar shape of the lower electrode. The density distribution of the current injected into the first electrode may be adjusted by, for example, disposing a current stop layer partially between the lower electrode 600 and the DBR layer 4 in a conventional surface emitting laser.
FIG. 3 is a diagram for explaining a specific example of such a current stop layer.

  The current stop layer shown in FIG. 3A is composed of the insulating layer 11 formed between the lower electrode 600 and the DBR layer 4 and having a plurality of holes.

  A large-diameter hole 11a is formed in the insulating layer 11 at a portion corresponding to the center portion of the lower electrode 600, and a plurality of medium-diameter holes 11b having a smaller diameter are formed around the large-diameter hole 11a. In addition, a plurality of small-diameter holes 11c having a smaller diameter are formed outside the medium-diameter hole 11b.

  By disposing the insulating film 11 in which a plurality of holes are formed in this manner between the lower electrode 600 and the DBR layer 4, the lower electrode 600 and the DBR layer 4 are brought into contact with each other as in the first embodiment. The closer the surface density of the portion is to the central portion, the larger the density, so that the density distribution of carriers injected into the active layer of the surface emitting laser can be made to be a distribution corresponding to the light power distribution in the active layer.

  The current stop layer shown in FIG. 3B is formed of an insulating layer 12 formed between the lower electrode 600 and the DBR layer 4 and having a plurality of holes.

  A large-diameter hole 12a is formed in the insulating layer 12 at a portion corresponding to the center portion of the lower electrode, and a plurality of small-diameter holes 12b having a small diameter are formed outside the large-diameter hole 12a. As the distance from the center of the lower electrode 600 increases, the density of the holes 12b decreases.

  By disposing the insulating film 12 in which a plurality of holes are formed in this manner between the lower electrode 600 and the DBR layer 4, the lower electrode 600 and the DBR layer 4 are brought into contact with each other as in the first embodiment. The closer the surface density of the portion is to the central portion, the higher the density, so that the density distribution of carriers injected into the active layer of the surface emitting laser can be made to be a distribution corresponding to the light power distribution in the active layer.

  In addition, as shown in FIGS. 3A and 3B, the electrode structure in which the current stop layer is disposed between the lower electrode and the DBR layer is easy to form the lower electrode. Since the area of the lower electrode can be increased, the contact area where the lower electrode is joined to an external heat sink via solder is also increased. Therefore, the electrode structure using the current stop layer shown in FIG. 3A or FIG. 3B is excellent in heat dissipation effect and superior in high output.

  Further, the electrode structure shown in FIG. 3A or 3B may have a resistance layer having an in-plane distribution of resistance values instead of the current stop layer.

  In this case, the resistance distribution of the resistance layer in the electrode structure is such that the resistance value decreases as the distance from the center of the lower electrode increases. As a result, the density distribution of carriers injected into the active layer of the surface emitting laser can be made to be a distribution corresponding to the light power distribution in the active layer.

  Furthermore, the electrode structure that connects the lower electrode and the DBR layer is not limited to the one having the current stop layer and the resistance layer, and the lower electrode itself may have an in-plane distribution of resistance values. Good. In this case, the resistance distribution of the lower electrode has a resistance value that decreases as the distance from the center increases. As a result, the density distribution of carriers injected into the active layer of the surface emitting laser can be made to be a distribution corresponding to the light power distribution in the active layer.

  In the first embodiment, the semiconductor substrate constituting the surface emitting laser is made of a semiconductor made of a nitrogen compound containing GaN as a main component, but the semiconductor substrate of the surface emitting laser is, for example, an SiC substrate or the like. The III-V nitride semiconductor material may be epitaxially grown thereon.

  Further, the surface emitting laser of the present invention is not limited to the one made of the above-described III-V group nitride semiconductor material. For example, the constituent material of the surface emitting laser may be an AlGaAs-based, AlGaInP-based semiconductor material, or a ZnSe-based semiconductor material. Even when such a semiconductor material is used, the high-frequency laser oscillation in a stable fundamental transverse mode is possible. An output surface emitting laser can be realized. In particular, when an AlGaInP-based semiconductor material is formed on a GaAs substrate whose substrate plane orientation is inclined from (100) to the [0-11] or [011] direction, the bandgap fluctuation due to crystal ordering does not occur. By using an AlGaInP-based semiconductor material, a surface emitting laser capable of stable high output operation can be realized.

  In the first embodiment, a recess 9 is formed by etching a region facing the lower electrode 6 of the semiconductor substrate 2a from the back surface side to the vicinity of the active layer 3 on the substrate surface side. Although the ring-shaped upper electrode 5 is formed on the back surface of the substrate so as to surround, the upper electrode 5 is not limited to the ring-shaped one formed on the back surface side of the semiconductor substrate 2a, but is formed on the bottom surface of the recess 9, for example. A transparent electrode may be used. When such a transparent electrode is used, the active layer and the upper electrode are brought closer to each other, so that the loss of the injection current into the active layer can be more effectively reduced.

  In the first embodiment, the recess 9 is formed by etching the region facing the lower electrode 6 of the semiconductor substrate 2a from the back surface side to the vicinity of the active layer 3 on the substrate surface side. When a material having a high conductivity and transparent to the laser light is used as the material for the semiconductor substrate of the surface emitting laser, the concave portion 9 does not need to be formed.

  In the first embodiment, as a surface emitting laser, a resonator includes a DBR layer 4 that is one of a plurality of semiconductor layers stacked on the semiconductor substrate 2a, and an external mirror that is disposed apart from the semiconductor substrate 2a. However, the surface-emitting laser may be a normal thin-film surface-emitting laser in which a resonator is formed by a semiconductor layer stacked on a semiconductor substrate. As in the first embodiment, the planar shape of the lower electrode 6 is such that current injection from the lower electrode 6 to the active layer has a high current density in the central portion of the lower electrode and a low current in the peripheral portion. By adopting a shape that is performed at a high density, it is possible to dramatically improve the high output characteristics.

  In the first embodiment, the surface emitting laser is one laser element having one surface emitting portion, but the surface emitting laser that is one laser element is a multi-beam type having a plurality of surface emitting portions. The surface emitting laser may be used. In this case, the saturation of the gain in each surface emitting portion is achieved by setting the density distribution of carriers injected into the active layer in each surface emitting portion of the surface emitting laser according to the light power distribution in the active layer. Can be mitigated, and a semiconductor laser having a higher output than the surface emission of laser light can be realized.

(Embodiment 2)
4A and 4B are diagrams for explaining a surface emitting laser according to Embodiment 2 of the present invention. FIG. 4A shows the cross-sectional structure, FIG. 4B shows the shape of the lower electrode, and FIG. c) shows the light intensity distribution in the light emitting region of the active layer. In FIG. 4, the same reference numerals as those in FIG. 1 are the same as those in the surface emitting laser of the first embodiment.

  The surface-emitting laser 100b according to the second embodiment includes a lower electrode 60 divided into two in place of the star-shaped lower electrode 6 in the surface-emitting laser 100a according to the first embodiment. In the surface emitting laser 100b, the surface of the recess 9 formed on the back surface side of the semiconductor substrate 2a is provided with a non-reflective coating so as to reduce the light loss in the resonator.

  Here, as shown in FIG. 4B, the lower electrode 60 includes a circular inner electrode portion 60a located at the center thereof and a ring-shaped outer electrode portion arranged so as to surround the inner electrode portion 60a. 60b. Further, a portion of the lower electrode 60 divided into two parts between the outer electrode portion 60b and the inner electrode portion 60a is a resistance separating portion 61 having a high resistance value. Thus, by making the lower electrode 60 into two parts, the density distribution of the current injected into the active layer 3 can be adjusted according to the light intensity distribution in the active layer 3.

  That is, as shown in FIG. 4C, the light intensity distribution in the active layer 3 has the highest light intensity Cd2 at the center of the light emitting region, that is, at the center of the region of the active layer 3 facing the lower electrode. It is close to a Gaussian distribution that decreases with increasing distance from the center. Therefore, in the surface emitting laser 100b of the second embodiment, the laser driving voltage applied to the inner electrode portion 60a is set to the outer side so that the density distribution of the current injected into the active layer 3 corresponds to the light intensity distribution. It is higher than the laser drive voltage applied to the electrode part 60b. In the surface emitting laser 100b, the laser driving voltage applied to the outer electrode portion 60b is obtained by superimposing a high frequency component on a direct current component so that the coherence of the generated laser light is reduced.

Next, the function and effect will be described.
The basic laser oscillation operation of the surface emitting laser 100b according to the second embodiment is performed in the same manner as the surface emitting laser 100a according to the first embodiment.

In the second embodiment, since the laser driving voltage on which the high frequency component is superimposed is applied to the outer electrode portion 60b of the divided lower electrode 60, the active electrode 3 faces the outer electrode portion 60b. The carrier density fluctuates in the part where For this reason, the laser oscillation state in the entire resonator varies, and temporal coherence is reduced.
Next, the characteristics of the surface emitting laser according to the second embodiment will be described in comparison with the conventional one.

  In the conventional surface-emitting laser, as described above, the lower electrode has a single electrode structure, so that at the time of high output, the lateral mode becomes multi-mode and the mode becomes unstable, thereby realizing a stable lateral mode. It was difficult.

  On the other hand, in the surface emitting laser 100b of the second embodiment, the lower electrode 60 is divided into two as shown in FIG. 4B, so that the density distribution of carriers injected into the active layer can be obtained. It is possible to approximate the light intensity distribution in the active layer, thereby realizing a surface emitting laser having excellent high output characteristics, which greatly improves the transverse mode stability at high output. .

  Further, in the second embodiment, the resonator of the surface emitting laser 100a is constituted by the DBR layer 4 formed on the semiconductor substrate 2a and the external mirror 1 arranged away from the semiconductor substrate 2a. Similar to the first embodiment, a sufficient resonator length can be secured. Thereby, the stability of the transverse mode of the resonator can be increased, and the light distribution in the active layer 3 in the vicinity of the lower electrode 60 can be increased.

  In addition, in a surface emitting laser having a resonator having an external active mirror and having a large effective active layer area, the problem of the consistency between the light intensity distribution and the injected carrier distribution in the active layer 3 becomes significant. In Embodiment 2, since the lower electrode of the surface emitting laser has a two-part structure, the problem of mismatch between the carrier density distribution and the light intensity distribution in the external mirror type surface emitting laser is solved, and the surface emitting laser has a high output. The characteristics are greatly improved.

  Further, even in a surface emitting laser in which the lower electrode is divided into a plurality of parts, if the effective active layer area is small, it is difficult to form the injected carrier density distribution by dividing the lower electrode, and the resistance separation layer portion between the separated electrodes In the second embodiment, however, the active layer area is sufficiently large by using the external mirror 1 as described above. For this reason, the injection current caused by the resistance separation layer is used. Since the problem of loss is almost negligible, the two-part structure of the lower electrode is effective.

  Further, in the second embodiment, the characteristics are greatly improved by changing the characteristics of the current injected into each divided electrode part. In particular, with conventional surface emitting lasers, it has been difficult to drive stably, modulate laser light, or superimpose a high-frequency component on the laser driving current when used with a large output of 100 mW or more. These problems are also solved in the surface emitting laser of the second embodiment.

  Here, a mechanism for preventing the generation of noise due to the return light in the surface emitting laser according to the second embodiment will be described.

  The return light noise is a phenomenon in which the noise is greatly increased by the light emitted from the semiconductor laser returning to the active layer. In order to prevent this, a method of reducing the coherence of light is usually employed. As one of them, there is a method of superimposing an RF signal of about several hundred MHz on the drive current. However, the conventional high-power semiconductor laser has a problem in that the required RF power is greatly increased due to an increase in driving current. Such an increase in the RF power greatly increases the cost of the entire system due to the increase in power consumption and the necessity of measures for heat dissipation and radiation.

  The surface emitting laser 100b according to the second embodiment solves the problem of high-frequency superposition in such a high-power laser.

  That is, the high frequency superposition is to change the state of the carrier density of the semiconductor laser, thereby changing the light oscillation state with time and reducing temporal coherence. Therefore, the rate of change with respect to the density of carriers injected into the active layer is important.

  In conventional surface emitting lasers with a single electrode structure, the injected current is dispersed throughout the electrode. Therefore, in order to change the injected carrier density greatly, the ratio of the current changed at a high frequency is increased with respect to the injected current. Therefore, the RF amplitude of the high-frequency component superimposed on the laser drive current is large.

  On the other hand, in the surface emitting laser 100b according to the second embodiment, the lower electrode 60 is divided into a plurality of electrode portions, and RF is superimposed on only some of the electrode portions. In the surface emitting laser 100b having such a configuration, since the lower electrode is divided into a plurality of parts, the injection current due to each electrode portion is significantly lower than the injection current due to the entire lower electrode. That is, the RF amplitude when the RF signal is superimposed on a part of the plurality of electrode portions obtained by dividing the lower electrode is a fraction of the RF amplitude when the RF signal is superimposed on a single lower electrode. This can greatly reduce the power of high frequency superposition. In addition, even when an RF signal is superimposed on a part of the electrode part, since the fluctuation of the injected carrier density by the electrode part can be sufficiently obtained, the oscillation state of the entire resonator changes and the temporal coherence can be lowered. it can.

  Furthermore, in the surface emitting laser 100b of the second embodiment, as shown in the light intensity distribution diagram of FIG. 4C, when a high output is obtained, a large current is applied to the electrode unit 60a located near the center of the light emitting region. However, only a small current corresponding to the power density of the light is required in the peripheral electrode part 60b far from the center of the light emitting region. For this reason, by superimposing the RF signal on the laser drive current supplied to the electrode part located near the periphery of the light emitting region, the coherence can be reduced efficiently with low RF power, resulting in the miniaturization of the system. Thus, cost reduction and power consumption can be reduced.

  In addition, the structure of the second embodiment in which the electrodes are divided is particularly effective for a GaN laser, and will be briefly described below.

  When a semiconductor laser based on a GaN substrate has a large relaxation oscillation and high frequency superposition is performed, spike noise is generated. This is a phenomenon in which when the current injected into the semiconductor laser is modulated with a high-frequency signal, the output light waveform changes in a spike shape due to relaxation oscillation, and a pulse output many times higher than the modulation degree is generated. In an optical disk system using a GaN laser, a high-frequency signal is superimposed on a laser drive current in order to prevent laser noise from increasing due to return light during reproduction of the optical disk. However, since the GaN laser produces a spike-like output with a high spire value even when the average power during reproduction is low, this causes the problem of degradation of the reproduction light that deteriorates the data recorded during reproduction. appear.

  On the other hand, in the configuration in which the electrode is divided into a plurality of parts and a high frequency signal is superimposed on a part of the electrode part, the spire output spire value is greatly reduced to less than half while the laser return light noise is reduced. I understood that I could do it.

  Therefore, the surface emitting laser 100b according to the second embodiment in which the lower electrode is divided into a plurality of parts is preferable for application to an optical disk device or the like.

  In addition, even a laser other than a GaN-based laser, for example, a semiconductor laser using an AlGaAs-based semiconductor material or an AlGaInP-based semiconductor material, can efficiently superimpose a high-frequency signal on a laser drive current as a structure in which electrodes are divided. Is possible.

  Furthermore, the configuration of the second embodiment in which the lower electrode is divided into a plurality of parts plays an effective role even when the output of the surface emitting laser is modulated.

  Currently, when modulating the output of a semiconductor laser, the entire laser drive current is modulated. However, when the entire driving current of the semiconductor laser is changed, a chirping phenomenon in which the oscillation wavelength varies due to a change in the temperature of the semiconductor laser due to an increase in power consumption occurs. For example, when recording on a medium such as an optical disk, recording is performed while modulating the light source light. At this time, if the wavelength of the light source light fluctuates due to chirping, the size of the focused spot changes due to the influence of chromatic aberration. To do. This phenomenon is particularly remarkable in a short wavelength region where the dispersion characteristics of the optical system are remarkable.

  The surface emitting laser 100b according to the second embodiment is effective in suppressing such a chirping phenomenon, and has a structure in which the lower electrode is divided into two electrode portions, and the current injected into one electrode portion. By modulating, the variation of the injection current in the entire laser accompanying the modulation of the injection current is reduced, and chirping can be suppressed to a low level.

  As described above, in the second embodiment, the lower electrode 60 is divided into the inner electrode portion 60a and the outer electrode portion 60b, and the laser driving voltage in which the high frequency signal is superimposed on the outer electrode portion far from the center of the light emitting region. Therefore, the density distribution of carriers injected into the active layer of the surface emitting laser can be made to be a distribution according to the light intensity distribution in the active layer.

  Specifically, as compared with a conventional surface emitting laser having a single-structure electrode, it is possible to inject more carriers into the emission center portion even at the same injection current value, and an electrode far from the emission center. The phenomenon in which the density of carriers injected from the portion into the active layer becomes extremely high can be alleviated. As a result, by improving the slope efficiency, it is possible to reduce the injected carrier density and improve the saturation level of the optical output.

  Furthermore, the effect of increasing the light output by the electrode structure divided into a plurality of in the surface emitting laser of the second embodiment is particularly effective in a gallium nitride surface emitting laser having a high threshold carrier density and a high differential gain. is there.

  In the second embodiment, the lower electrode 60 has a two-divided structure, but the lower electrode may have a more finely divided structure. At this time, the plurality of divided electrode portions are arranged substantially uniformly around the emission center of the laser beam. Thereby, the carrier density in the active layers having different light intensity distributions can be made uniform easily, and more stable single transverse mode operation can be realized at high output.

  Further, the surface emitting laser according to the second embodiment is not limited to the one made of the above-described III-V group nitride semiconductor material. For example, the constituent material of the surface emitting laser according to the second embodiment may be an AlGaAs-based, AlGaInP-based semiconductor material, or a ZnSe-based semiconductor material. Even when such a semiconductor material is used, a plurality of lower electrodes are provided. With the divided structure, it is possible to realize a high-power semiconductor laser that performs laser oscillation in a stable fundamental transverse mode.

  In the first embodiment or the second embodiment, the single surface emitting laser formed on the semiconductor substrate has been described. However, the surface emitting laser 100a according to the first embodiment or the embodiment is formed on one semiconductor substrate. A plurality of the surface emitting lasers 100b of the second embodiment may be formed.

  FIG. 5 is a diagram showing a specific example of a semiconductor laser device in which a plurality of surface emitting lasers are formed on one semiconductor substrate. FIG. 5 (a) shows the shape of the lower electrode, and FIG. Vb-Vb sectional drawing is shown.

  As shown in FIG. 5A, the semiconductor laser device 120 is formed by forming a plurality of surface-emitting lasers 120b identical to the surface-emitting laser of the second embodiment on one semiconductor substrate 22.

  Specifically, as shown in FIG. 5B, an active layer 23 and a DBR layer 24 are stacked on the surface of the semiconductor substrate 22. A separation groove 62 a that reaches the inside of the substrate from the surface side of the DBR layer 24 is formed on the surface side of the semiconductor substrate 22, and an insulating material is embedded in the separation groove to form a resistance separation region 62. A plurality of the separation grooves 62a are formed in the vertical direction and the horizontal direction, and the lower electrode 26 divided into two is arranged on the region surrounded by the separation grooves 62a, like the lower electrode in the second embodiment. Yes.

  Further, a ring-shaped upper electrode 25 is formed on the other surface of the semiconductor substrate 22 so as to face the lower electrode 26, and a concave portion 29 by etching is formed on an inner portion of the upper electrode 25 of the substrate 22. Is formed. Further, an external mirror 21 is disposed above the upper electrode 25.

  Thus, by forming a plurality of surface emitting lasers 120b in one substrate and separating the adjacent surface emitting lasers 120b by the resistance isolation region 62, it becomes possible to achieve high output, and the adjacent surfaces Mutual influence between the light emitting lasers 120 b can be avoided by the resistance isolation region 62.

(Embodiment 3)
FIG. 6 is a schematic configuration diagram illustrating a laser projection apparatus according to Embodiment 3 of the present invention.

  The laser projector 130 according to the third embodiment includes a laser light source 131, a lens 132 that collimates laser light emitted from the laser light source 131, and a spatial modulator 133 that spatially modulates the collimated laser light. And a projection lens 134 that projects the modulated laser beam onto the screen 135. In the laser projector 130 of the third embodiment, the same laser light source as the surface emitting laser 100b of the second embodiment in which the lower electrode is divided into a plurality of parts is used. In the surface-emitting laser that is the laser light source of the third embodiment, the current injected from the partial electrode portion of the lower electrode into the active layer of the lower electrode is modulated, and further, the plurality of electrodes The RF signal is superimposed on the current injected into a part of the part. In particular, in the surface emitting laser of this embodiment, high frequency signals having different frequencies are superimposed on the inner electrode portion and the outer electrode portion.

Next, the function and effect will be described.
Hereinafter, first, the configuration of a semiconductor laser applied to a laser display which is a kind of such a laser projection apparatus will be described.

  The laser display is a display device using RGB laser light, and a large output of several hundred mW to several watts or more is required as a laser output.

  Therefore, consider a case where the surface emitting lasers of the first and second embodiments are applied to a laser display which is a kind of the laser projection apparatus of the third embodiment.

The surface emitting lasers of the first and second embodiments have the following features.
The first feature is that high output is easy and stable single transverse mode oscillation can be performed.

  In addition, the second feature is that the beam shape is close to an ideal circle, and therefore, a converging beam for a laser display can be realized with a simple optical system without requiring a shaping optical system. It is. In particular, the surface emitting laser 100b of the second embodiment is capable of performing high-power optical modulation.

  Although it is very effective to apply a surface emitting laser having such output characteristics to a laser display, in order to use it as a light source for a laser display, the following characteristics are required in addition to the above output characteristics. The

  First, wavelength stability is required. In particular, in a red laser, the wavelength change of the visibility is large, so it is necessary to suppress the wavelength change to ± 1 nm or less.

  Moreover, in order to reduce speckle noise, it is important to reduce coherence, and it is necessary to expand the wavelength spectrum width to several nm.

  In the third embodiment, the above two problems, that is, the point of suppressing the wavelength change and the point of expanding the wavelength spectrum width have been solved, and will be described in comparison with the conventional one.

First, wavelength stabilization will be described.
When an image is projected by laser light, it is necessary to modulate the laser output intensity according to the gradation. At this time, the problem is the mode stability and wavelength change as well as the output intensity. That is, in the laser display, it is necessary to modulate the laser light from 100 mW to a value of several mW or less. At this time, the laser wavelength changes with the output intensity. Therefore, in the conventional high-power semiconductor laser, the driving current differs greatly between high output and low output, so that chirping with significantly different oscillation wavelengths occurs due to the difference in laser temperature.

  On the other hand, the surface emitting laser that is the laser light source of the laser projector 130 according to the third embodiment divides the lower electrode into a plurality of electrode portions as shown in FIG. By modulating the current injected into the substrate, changes in the injected current can be reduced, and stable modulation can be performed with little wavelength fluctuation. Further, in this surface emitting laser, the gradation can be increased by stabilizing the transverse mode.

Next, expansion of the wavelength spectrum width for reducing speckle noise will be described.
Since a laser display light source requires high output characteristics, it is necessary to perform high-frequency superposition while maintaining an average output at 100 mW or more.

  Therefore, in the conventional semiconductor laser, it is necessary to perform high-frequency superimposition while injecting a current of several hundred mA, and a high-power high-frequency circuit for applying a high-frequency signal having a current amplitude of several hundred mA is required. However, since very large power consumption is required, reduction of power consumption and reduction of external radiation are problems.

  In contrast, in the surface emitting laser as the laser light source according to the third embodiment, the RF current can be reduced by superimposing the RF signal on the current injected into a part of the plurality of divided electrode portions. In the portion of the active layer that is away from the center of the light emitting region, the current density can be reduced, thereby reducing the injection current. As a result, the amplitude of the superimposed RF signal that depends on the injected current can be greatly reduced, and the system can be simplified, reduced in size, and reduced in power consumption.

Next, prevention of speckle noise by further reducing coherence will be described.
Since the decrease in coherence is proportional to the expansion of the spectrum width, the speckle noise can be further reduced if the spectrum width is greatly increased. In order to realize this, it is effective to increase the power of the high-frequency current superimposed on the driving current of the semiconductor laser, but the spectral width expansion due to the power increase of the superimposed high-frequency current is about several nm in wavelength. Limited to.

  Therefore, in the surface emitting laser as the laser light source of the third embodiment, high-frequency signals with different frequencies are applied to the divided inner electrode portion and outer electrode portion so that the spectrum width is further expanded.

  For example, if a high frequency signal of 500 MHz is applied to one of the inner electrode portion and the outer electrode portion and a high frequency signal of 400 MHz is applied to the other, the relative disturbance of the oscillation state due to the injected current from each electrode portion increases. The spread of the spectrum width is increased. At this time, although the increase in the spectrum width is frequency-dependent, the amount of increase in the spectrum width can be increased by 1.2 to 1.5 times compared to the case where a high frequency signal is applied to one electrode.

  The split electrode structure of the surface emitting laser according to the second embodiment used in the laser projection device 130 according to the third embodiment is particularly effective for reducing the coherence of high output light of 100 mW or more.

  Further, in the surface emitting laser used in the laser projection apparatus of the third embodiment, it is possible to reduce speckle noise by changing the oscillation wavelength by self-excited oscillation using supersaturated absorption. The self-excited oscillation is an oscillation state in which laser light is emitted in a pulsed manner despite a direct current flowing through the semiconductor laser.

  That is, since self-excited oscillation uses supersaturated absorption, it was difficult to apply it to a high-power semiconductor laser. However, the surface emitting laser used in the laser projection apparatus of Embodiment 3 has a lower electrode that is connected to an inner electrode portion and an outer electrode. Since it has a structure divided into two parts with the electrode part, high output surface emission can be achieved by providing a saturable absorber in the part of the active layer corresponding to the periphery of the lower electrode where the injection current density is reduced. In the laser, speckle noise can be reduced by self-excited oscillation using supersaturated absorption.

  As described above, in the third embodiment, as the laser light source of the laser projection apparatus, a surface emitting laser having a structure in which the lower electrode is divided into the inner electrode portion and the outer electrode portion is used as in the second embodiment. The density of current injected into the layer can be matched to the light intensity distribution in the active layer, and the current density can be reduced in the portion of the active layer away from the center of the light emitting region, The injection current can be reduced.

In the third embodiment, the RF current can be reduced by superimposing the RF signal on the current injected into the active layer from some of the divided electrodes.
As a result, it is possible to realize simplification, miniaturization, and low power consumption of the laser projection apparatus.

(Embodiment 4)
FIG. 7 is a diagram for explaining a surface emitting laser according to Embodiment 4 of the present invention, and shows a cross-sectional structure of the surface emitting laser. In FIG. 7, the same reference numerals as those in FIG. 1 are the same as those in the surface emitting laser according to the first embodiment.

  The surface emitting laser 100d according to the fourth embodiment includes an external mirror 10 having concave surfaces on both sides, instead of the external mirror 1 in the surface emitting laser 100a according to the first embodiment.

Next, the function and effect will be described.
A surface emitting laser has a small divergence angle of emitted light and can be easily coupled to an optical system such as a fiber. However, in order to reduce the size of the bulk optical system using an external lens or the like, the characteristic that the spread angle of the emitted light is small is not preferable. This is because when the emitted light from the surface emitting laser is collimated or condensed by the lens system, the distance required to spread the light to the effective diameter of the lens becomes long.

  On the other hand, as shown in FIG. 7, the surface emitting laser 100d according to the fourth embodiment is configured such that both surfaces of the external mirror 10 are concave and the spread angle of the outgoing light 8 is increased. Therefore, the surface-emitting laser 100d according to the fourth embodiment has a short distance required for the emitted light to spread to the effective diameter of the lens, and is effective for reducing the size of the bulk optical system.

(Embodiment 5)
8A and 8B are diagrams showing an example of a laser module according to Embodiment 5 of the present invention, in which FIG. 8A is a side view and FIG. 8B is a plan view.

  The laser module 150 of the fifth embodiment is useful as a small RGB light source for application to a laser display.

  This laser module 150 is formed by mounting a surface emitting laser on a package, and three surface emitting lasers 101 to 103 are mounted on a base member 151 of the package. The back surface of the base member 151 is a heat radiating surface, and the lead terminals 101a, 102a, and 103a of the surface emitting lasers 101, 102, and 103 are taken out from the back surface side of the base member 151.

  Here, each of the surface emitting lasers 101 to 103 has the same configuration as the surface emitting laser described in any of Embodiments 1 to 4, and the surface emitting laser 101 is a red surface emitting laser or a surface emitting laser. Reference numeral 102 denotes a green surface emitting laser, and the surface emitting laser 103 is a blue surface emitting laser. These three surface-emitting lasers on the base member 151 are arranged at equal intervals on one circumference with the center of the package as the center.

Next, the function and effect will be described.
To realize a small laser display, it is essential to reduce the size of the light source. In order to realize this, it is effective to use the surface emitting laser described in the first to fourth embodiments as a light source.

  Since the surface emitting lasers mentioned in the first to fourth embodiments have an external mirror, the output can be increased. In addition, these surface emitting lasers have an active layer located in the vicinity of the lower electrode, and therefore have excellent heat dissipation characteristics and are advantageous in generating high output. Further, the surface emitting laser has characteristics such as no deterioration of the end face and excellent reliability because the light power density at the end face on the substrate side is low. In particular, the surface emitting laser according to the second embodiment is advantageous in that the high output characteristics can be dramatically improved by the electrode division structure.

  Furthermore, the surface emitting laser is effective for realizing a modularized multi-wavelength integrated light source. Specifically, the surface-emitting laser can dissipate the bottom surface, that is, dissipate from the surface opposite to the laser light emission surface, so that different surface-emitting lasers are mounted in a single package as shown in FIG. In this case, the package structure becomes very simple and the cost can be reduced. Further, in the multi-wavelength integrated light source that is a laser module, heat radiation can be performed from the back surface of the package, and laser output can be extracted from the front surface of the package.

  As described above, in the fifth embodiment, the three surface emitting lasers 101, 102, 103 of red, green, and blue having the same configuration as the surface emitting laser described in any of the above embodiments are included in the package. Since the laser module is configured by mounting, a small integrated light source can be obtained, and as a result, an ultra-small laser irradiation apparatus can be realized.

  In the fifth embodiment, a multi-wavelength light source that outputs three wavelengths of laser light is shown as a laser module in which a surface emitting laser is mounted on a package. However, the multi-wavelength light source has two wavelengths. Even a thing with four or more wavelengths may be sufficient.

  Further, the number of surface emitting lasers constituting the laser module and the arrangement of the surface emitting lasers in the package are not limited to those of the fifth embodiment.

  FIGS. 9A and 9B are diagrams showing a modification of the number and arrangement of surface emitting lasers in the laser module of the fifth embodiment. FIG. 9A is a side view and FIG. 9B is a plan view.

  A laser module 150a shown in FIG. 9 realizes an RGB three-wavelength laser light source, similar to the laser module 150 shown in FIG.

  This laser module 150a is formed by mounting four surface emitting lasers on a package, and two green surface emitting lasers 106 and 107 are provided at the center of a package base member 151. It arrange | positions so that it may be located on an axis line. A red surface emitting laser 104 and a blue surface emitting laser 105 are arranged on another axis passing through the center of the package and perpendicular to the axis so as to sandwich the two green surface emitting lasers. Here, each of the surface emitting lasers has the same configuration as any of the surface emitting lasers of the first to fourth embodiments, and the arrangement of the four surface emitting lasers on the base member is relative to the center of the package. Are symmetrically arranged.

  The back surface of the base member 151 is a heat dissipation surface, and the lead terminals 104a, 105a, 106a, and 107a of the surface emitting lasers 104, 105, 106, and 107 are taken out from the back surface side of the base member 151. It is.

  In a laser module as an RGB light source that generates such red, green, and blue three-wavelength laser beams, the arrangement of the surface emitting lasers of the respective colors is important. That is, when an RGB light source is realized by a surface emitting laser, a green light source is particularly difficult to achieve high output. The green light source is usually realized by a ZnSe laser material, but its lifetime is reduced at high output. For this reason, it must be used at a relatively low output.

  Therefore, in the laser module 150 shown in FIG. 9, as shown in FIG. 9B, two green surface emitting lasers 104 and 105 are used and arranged close to each other, and the green surface emitting lasers of these green surface emitting lasers are arranged. A red surface emitting laser 106 and a blue surface emitting laser 107 are disposed on both sides. As a result, high output and long life of the laser light source can be realized.

  Further, the laser module 150 according to the fifth embodiment shown in FIG. 8 that is an RGB light source and the laser module 150a in which the number and arrangement of the surface emitting lasers in the laser module 150 are changed include a liquid crystal panel or a DLP (digital light Laser irradiation device that modulates the light emitted from the RGB light source with a two-dimensional spatial modulation element and projects the image by combining it with a two-dimensional spatial modulation element such as DMD (digital micromirror device) used in processing And can be applied to a laser display.

(Embodiment 6)
FIG. 10 is a diagram for explaining a semiconductor laser device according to a sixth embodiment of the present invention.

  The semiconductor laser device 160 includes a surface emitting laser that emits surface light from a laser beam, and a wavelength conversion element 161 that is disposed in a resonator of the surface emitting laser and converts the wavelength of the laser light from the surface emitting laser. Yes.

  Here, the surface emitting laser has the same configuration as the surface emitting laser 100a of the first embodiment. However, the surface emitting laser in this semiconductor laser device is not limited to the surface emitting laser of the first embodiment, and may be the surface emitting laser described in any of the second to fourth embodiments.

  The wavelength converting element 161 is made of a nonlinear optical crystal member disposed between the external mirror 1 constituting the resonator and the active layer 3 formed on the semiconductor substrate 2a.

Here, as the nonlinear optical crystal material, KTiOPO ₄ or polarization inversion MgOLiNbO ₃ is preferable. In particular, since the polarization inversion MgOLiNbO ₃ has a large non-linear constant, the element length of the wavelength conversion element can be shortened, which is convenient for insertion into a resonator having a relatively short distance from the external mirror.

Next, the function and effect will be described.
The semiconductor laser device 160 according to the sixth embodiment can output laser light having a short wavelength by converting the wavelength of laser light generated by a surface emitting laser by the wavelength conversion element 161.

  Hereinafter, features of the semiconductor laser device 160 of the present embodiment will be briefly described.

  Since the wavelength conversion element generally has a narrow convertible wavelength tolerance, the wavelength of the fundamental wave that causes laser oscillation and the stability of the transverse mode greatly affect the wavelength conversion efficiency. In addition, in a normal surface emitting laser, when the single mode property of the transverse mode is deteriorated or changed, there is a problem that the conversion efficiency is greatly reduced or changed.

  In contrast, the semiconductor laser device of the sixth embodiment can achieve excellent stability and high efficiency.

  That is, since the nonlinear optical crystal member constituting the wavelength conversion element is arranged in the resonator, the power density of light incident on the nonlinear optical crystal member is increased, and high-efficiency conversion by the wavelength conversion element is possible. .

  In the sixth embodiment, the semiconductor laser device in which the surface emitting laser and the wavelength conversion element are combined has been shown in which the wavelength conversion element is disposed in the resonator of the surface emitting laser. You may arrange | position outside a resonator.

  FIG. 11 is a diagram showing a modified arrangement of wavelength conversion elements in the semiconductor laser device of the sixth embodiment.

  A semiconductor laser device 160a shown in FIG. 11 has a wavelength conversion element 161a arranged outside the resonator, and the other configuration is the same as that of the semiconductor laser 160 of the sixth embodiment.

  Further, the wavelength conversion element in the semiconductor laser device shown in FIGS. 10 and 11 may be a waveguide type element or a bulk type element.

  However, since the conversion efficiency in the wavelength conversion element largely depends on the condensing characteristic of the fundamental wave, it is important to use a single transverse mode. Therefore, the semiconductor laser device that outputs the short wavelength light by converting the wavelength of the output light of the surface emitting laser can control the transverse mode to a single mode as shown in the sixth embodiment, and has a high output. It is necessary to be able to perform wavelength conversion.

(Embodiment 7)
FIG. 12 is a schematic configuration diagram illustrating a laser projection apparatus according to the seventh embodiment of the present invention.

  The laser projector 170 according to the seventh embodiment includes a laser light source 171 and a projection optical system 172 that projects laser light emitted from the laser light source 171 onto a screen 173. In the laser projector 170 according to the seventh embodiment, a laser light source having the same configuration as that of the surface emitting laser 100b according to the second embodiment is used. However, the surface emitting laser used as the laser light source of the laser projection device 170 is not limited to that of the second embodiment, and may be those shown in other embodiments.

  Hereinafter, a laser display which is a kind of such a laser projection apparatus will be described.

  The laser display is composed of an RGB light source and a projection optical system, and projects a full-color image by projecting light from the laser light source onto a screen or the like by the projection optical system. As a projection method, it is classified into a type of projecting on a projection body such as an external screen or a wall and viewing the reflected light, and a type of irradiating light from the back of the screen as a rear projection type and viewing the reflected light. In either case, the color is recognized by the light scattered by the screen or the like.

  However, when a conventional laser display uses a semiconductor laser with high coherence, there is a problem in that speckle noise is generated due to interference of light scattered by the screen. As an effective method for reducing speckle noise, there is a method for reducing the coherence of laser light. In order to reduce the coherence of the laser light, it is effective to make the longitudinal mode multi-mode. In particular, the speckle noise can be greatly reduced by expanding the spectrum width of the longitudinal mode.

  In the surface emitting laser used as the laser light source of the laser projection apparatus of the seventh embodiment, as shown in the second embodiment, the spectrum is obtained by superimposing a high-frequency signal on a part of the plurality of divided electrode portions. The width can be increased and the coherence can be reduced. In order to reduce speckle noise, it is necessary to expand the longitudinal mode spectrum width in terms of wavelength to 1 nm or more, and more desirably to about 5 nm or more.

  Further, the longitudinal mode spectrum width can be further expanded by using a method of applying high-frequency signals having different frequencies to different electrode portions.

  The oscillation wavelength of the RGB light source is important from the relationship between the wavelength used for the laser display and the visibility. The wavelength used and the required light intensity are determined by the effect of visibility. The width of wavelength and color reproducibility is determined by the influence of chromaticity.

  FIG. 13 shows the relationship between the wavelength of the blue light source and the required output. Here, when the red wavelength is fixed at 640 nm and the green color is fixed at 532 nm, the relationship between the blue wavelength and the necessary output is shown to achieve a brightness of 1000 lm on the screen.

  The blue light has a sharp increase in required power because the visibility decreases when the wavelength is 430 nm or less. Further, when the wavelength is 460 nm or more, it approaches the green region, so that the color range that can be expressed becomes narrow and at the same time, the necessary power for expressing blue increases. At the same time, the red power increases.

  On the other hand, a blue surface emitting laser using a GaN semiconductor is usually a high output laser in the vicinity of 410 nm. In order to shift this wavelength to the longer wavelength side, it is necessary to increase the amount of In added. However, if the amount of In added is increased, the crystal composition deteriorates due to segregation of In, and the reliability and high output characteristics deteriorate. . Therefore, it is desirable to set the wavelength to 455 nm or less in a blue laser using GaN. From the viewpoint of color reproducibility, it is preferable to use a blue light source having a short wavelength because the range of colors that can be expressed in the blue region is widened.

  From the above viewpoint, the wavelength region of the blue surface emitting laser is preferably a region of 430 nm to 455 nm. More preferably, the wavelength region is desired to be 440 to 450 nm. In this case, it is possible to realize low power consumption and high color reproducibility by reducing required power.

  The red surface emitting laser can be realized by an AlGaAs semiconductor material or an AlGaInP semiconductor material. However, in order to achieve high output, it is preferable to set the wavelength region to a region of 630 to 650. Furthermore, the wavelength region is most preferably in the range of 640 nm ± 5 nm from the viewpoint of expanding visibility and the wavelength range of blue light used.

  The green surface emitting laser can be realized with a ZnSe-based semiconductor material.

  That is, in the Fabry-Perot semiconductor laser, the optical power density in the waveguide is high, and it is difficult to obtain reliability when using a ZnSe-based semiconductor material. However, when the green laser is configured as the surface emitting laser of the present invention, the optical power density in the crystal can be reduced, and high reliability can be ensured. As a wavelength region considering the color balance of the green surface emitting laser, a wavelength region of 510 to 550 nm is necessary. However, in consideration of the reliability of the surface emitting laser, the wavelength region is desirably a region of 510 to 520 nm, and high reliability and high output characteristics can be realized in this region. The green surface emitting laser can also be realized by a semiconductor material in which GaN is doped with a large amount of In. Even in this case, a wavelength region of 500 to 520 nm is desirable.

  As described above, the surface emitting laser according to the present invention can suppress hole burning caused by the optical power density distribution in the light emitting region, and can reduce deterioration of high output characteristics such as instability of the transverse mode and reduction of gain. It is useful as a light source for optical recording devices, optical display devices and the like that require high-power semiconductor lasers, and is also useful for other applications such as laser processing and medical use.

  The present invention relates to a surface emitting laser and a laser projection device, and more particularly to a surface emitting laser that operates stably at a high output and a laser projection device using the surface emitting laser as a light source.

  Surface-emitting lasers are semiconductor lasers that perform laser oscillation at a low threshold and have excellent beam quality, and can be applied to the optical communication field using modulation characteristics that output light can be modulated at high speed. ing. However, there is a problem that it is difficult to increase the output as a problem of the surface emitting laser.

  Since the surface emitting laser is composed of a thin film, the resonator length is very short due to its structure. For this reason, it is difficult to increase the resonator length to obtain a sufficient gain.

  On the other hand, it is conceivable to increase the driving current of the surface emitting laser to increase the output, but in the surface emitting laser, when the carrier density in the active layer is too high, the light output is increased due to gain saturation due to spatial hole burning. Saturation impedes high light output operation.

  For this reason, it is effective to increase the beam cross-sectional area of the surface-emitting laser in order to increase the output of the surface-emitting laser without increasing the resonator length or driving current. Conceivable.

  However, in such a surface emitting laser with a short resonator length, if the beam cross-sectional area is increased in order to increase the output of the laser, the transverse mode in the resonator becomes multimode, and the beam quality is increased. In addition, there has been a problem that the oscillation efficiency is remarkably lowered.

  On the other hand, surface emitting lasers that have eliminated such beam quality and oscillation efficiency degradation have already been developed. For example, Patent Document 1 discloses that the surface emitting lasers have multiple transverse modes. An increase in beam cross-sectional area while suppressing is disclosed.

  14A and 14B are diagrams for explaining the surface emitting laser disclosed in Patent Document 1. FIG. 14A shows the cross-sectional structure, FIG. 14B shows the shape of the lower electrode, and FIG. (C) shows the light intensity distribution in the region facing the lower electrode of the active layer of this surface emitting laser.

  A surface emitting laser 200 shown in FIG. 14A has a semiconductor substrate 2, an active layer 3 formed on one surface of the semiconductor substrate 2, and a reflective layer 4 formed on the active layer 3. is doing. Here, the reflection layer 4 is a distributed Bragg reflection layer in which materials 4a and 4b having different refractive indexes are alternately stacked, and is also referred to as a DBR (Distributed Bragg Reflector) layer. The surface emitting laser 200 is formed so as to surround a circular lower electrode 600 formed on the surface of the DBR layer 4 and a region facing the lower electrode 600 on the other surface of the substrate 2. And an upper electrode 5 having a ring shape.

  The surface-emitting laser 200 has an external mirror 1 disposed above the surface electrode 5 so as to face the inner substrate surface. In the surface-emitting laser 200, the DBR layer 4 and an external The mirror 1 constitutes a resonator that amplifies the light generated in the active layer 3 so that laser oscillation occurs. Here, the DBR layer 4 is a total reflection layer, and the external mirror 1 is a partially transmissive mirror.

Next, the operation will be described.
In the surface emitting laser 200, when a driving voltage is applied between the upper electrode 5 and the lower electrode 600 and a current is injected into the active layer 3, light is generated in the active layer 3, and the generated light is resonant. Amplified by the instrument. When the magnitude of the injection current becomes a certain value, that is, larger than the laser oscillation threshold, laser oscillation occurs in the resonator, and the laser beam 8 is emitted to the outside via the external mirror 1. At this time, the laser light 8 is surface-emitted, and the emission direction of the laser light is a direction perpendicular to the surface of the substrate 2.

  As described above, in the surface emitting laser disclosed in Patent Document 1, one of the mirrors constituting the resonator is arranged as an external mirror 1 apart from the substrate to increase the resonator length. That is, by using such an external mirror 1, even if the beam cross-sectional area has a large value, the resonance mode can be made single, and high output characteristics are realized.

  Patent Document 2 discloses an electrode structure for making the carrier density in the active layer uniform in a surface emitting laser.

In the surface emitting laser disclosed in Patent Document 2, the distribution of the current injected into the active layer can be controlled by dividing the back electrode into a plurality of parts, thereby realizing a large surface emitting laser. Yes.
US Pat. No. 6,404,797 Japanese Patent Laid-Open No. 11-233889

  However, in the surface emitting laser 200 disclosed in Patent Document 1, the carrier density distribution in the active layer becomes a problem when realizing high output characteristics. That is, in the surface emitting laser 200 described in this document, the light intensity distribution in the region corresponding to the lower electrode 600 of the active layer 3 is a distribution close to a Gaussian distribution as shown in FIG. The light intensity Lp has a peak at the light emission center portion of the layer. On the other hand, in the region corresponding to the lower electrode 600 in the active layer 3 of the surface emitting laser 200, the light is not injected into the active layer 3 even though there is a large deviation in the light intensity distribution between the central portion and the peripheral portion. The carrier density Cd is uniform. For this reason, the density of carriers existing in the active layer is large in the peripheral portion of the central portion of the region corresponding to the lower electrode 600 of the active layer 3, and the carrier is in an excessive state. In the part, there is a shortage of carriers. Due to such a non-uniform distribution of carriers, a refractive index distribution is generated in the active layer 3 and the resonance mode becomes multi-dimensional. Furthermore, there is a concern about the occurrence of gain saturation.

This phenomenon is caused by an infrared semiconductor laser made of an AlGaAs-based semiconductor material (Al _x Ga _1-x As (0 ≦ x ≦ 1)) or an AlGaInP-based semiconductor material (Al _x Ga _y In _1-xy P (0 ≦ x Compared with a red semiconductor laser having a ≦ 1, 0 ≦ y ≦ 1)), this is particularly remarkable in a nitride semiconductor laser having a very high threshold carrier density and high differential gain.

  In addition, the surface emitting laser disclosed in Patent Document 2 has a problem in that efficiency is lowered due to a loss in current injected into the active layer due to a portion of the resistance separation layer that divides a plurality of electrodes.

  The present invention solves the conventional problems as described above, and can perform laser oscillation in a stable transverse mode, and can efficiently inject current into an active layer. It is an object of the present invention to provide a light emitting laser and a laser projection apparatus using such a high output surface emitting laser as a light source.

  In order to solve the above-described problem, a surface emitting laser according to claim 1 of the present invention is a surface emitting laser that performs surface emission of laser light, and includes an active layer formed on a semiconductor substrate, and the active layer. A pair of electrodes for injecting carriers, and one of the pair of electrodes is composed of one electrode layer, and current injection from the one electrode to the active layer is performed at the center of the one electrode. This is performed at different current densities in the portion and the peripheral portion.

  As a result, the density distribution of carriers injected into the active layer can be adjusted in accordance with the light intensity distribution in the active layer, and the carrier distribution in the active layer can be made uniform. It is possible to realize a surface emitting laser having excellent high output characteristics, in which lateral mode stability during output is greatly increased.

  A surface-emitting laser according to a second aspect of the present invention is the surface-emitting laser according to the first aspect, wherein the surface-emitting laser includes a semiconductor layer stack including the active layer formed by stacking a plurality of semiconductor layers on the semiconductor substrate. The surface density at which the electrode layer and the semiconductor layer laminate are in contact with each other is different between the central portion of the electrode layer and the peripheral portion thereof.

  As a result, the density distribution of carriers injected into the active layer can be adjusted by the contact area between the electrode layer and the semiconductor layer stack, and the carrier distribution in the active layer having a light intensity distribution can be made uniform. Can be realized by a simple method such as changing the shape of the electrode layer.

  A surface-emitting laser according to a third aspect of the present invention is the surface-emitting laser according to the first aspect, wherein the one electrode has a plurality of micro holes in an electrode layer constituting the one electrode, and the occupation density of the micro holes is The center portion of the one electrode and the peripheral portion thereof are formed differently.

  Accordingly, the density distribution of carriers injected into the active layer can be adjusted by changing the arrangement of the micro holes formed in the electrode layer and the size of the micro holes, and the active layer having a light intensity distribution. Uniform carrier distribution can be realized by simple modification of the structure of the electrode layer. In addition, the spread of the entire electrode layer on the semiconductor layer can be increased to further enhance the heat dissipation effect from the electrode layer to the heat sink, and a surface emitting laser having more excellent high output characteristics can be realized.

  A surface-emitting laser according to a fourth aspect of the present invention is the surface-emitting laser according to the first aspect, wherein the one electrode has a resistance value of an electrode layer constituting the one electrode and a central portion of the one electrode and its periphery. It is characterized by being different from the part.

  As a result, the density distribution of carriers injected into the active layer can be adjusted more precisely according to the light intensity distribution in the active layer by changing the electrode layer material and components to change the resistance value of the electrode layer. be able to.

  The surface-emitting laser according to claim 5 of the present invention is the surface-emitting laser according to claim 1, wherein a semiconductor layer stack including the active layer, which is formed by stacking a plurality of semiconductor layers on the semiconductor substrate, A resistance layer formed between the semiconductor layer stack and an electrode layer constituting the one electrode, and a resistance value of the resistance layer is a portion corresponding to a central portion of the one electrode; It differs in the part corresponding to the peripheral part, It is characterized by the above-mentioned.

  Thereby, the density distribution of carriers injected into the active layer can be adjusted more precisely according to the light intensity distribution in the active layer by changing the material and components of the resistance layer.

  A surface-emitting laser according to a sixth aspect of the present invention is the surface-emitting laser according to the first aspect, wherein the surface-emitting laser includes a semiconductor layer stack including the active layer formed by stacking a plurality of semiconductor layers on the semiconductor substrate. And a resonator for amplifying the light generated in the active layer so as to cause laser oscillation, and the reflective layer included in the semiconductor layer stack and the semiconductor layer stack so as to face the reflective layer It is characterized by comprising an external mirror.

  As a result, the cavity length of the surface emitting laser can be increased, the cross-sectional area of the surface emitting laser can be increased while suppressing the transverse mode in the resonator from becoming multimode, and the high output characteristics of the surface emitting laser. Can be dramatically improved.

  The surface-emitting laser according to claim 7 of the present invention is the surface-emitting laser according to claim 6, wherein the external mirror is a partially transmissive mirror having concave surfaces on both sides. is there.

  This increases the divergence angle of the surface emitting laser light from the surface emitting laser, and a general-purpose lens with a large aperture and a short focal length can be used for the optical system that couples the surface emitting laser to an optical fiber or the like. Thus, the optical system can be made compact with a low cost and a short optical path length.

  The surface-emitting laser according to claim 8 of the present invention is the surface-emitting laser according to claim 1, wherein the surface-emitting laser has a semiconductor layer stack including the active layer formed by stacking a plurality of semiconductor layers on the semiconductor substrate. The semiconductor layer stack includes a supersaturated absorber that is disposed in the vicinity of the active layer and absorbs supersaturated carriers in the active layer.

  As a result, the oscillation state of the surface emitting laser is changed to a self-excited oscillation state utilizing a phenomenon of absorbing supersaturated carriers, that is, an oscillation state in which laser light is emitted in a pulsed manner even though a direct current is flowing. Speckle noise can be reduced.

  The surface-emitting laser according to claim 9 of the present invention is the surface-emitting laser according to claim 1, wherein the oscillation wavelength of the surface-emitting laser light is a wavelength within a range of 430 to 455 nm. Is.

  Thereby, it is possible to obtain a blue surface emitting laser that realizes low power consumption by reducing required power and high color reproducibility.

The surface-emitting laser according to claim 10 of the present invention is the surface-emitting laser according to claim 1, wherein the oscillation wavelength of the surface-emitting laser light is a wavelength in the range of 630 to 650 nm. Is.
Thereby, a red surface emitting laser realizing high output can be obtained.

A surface-emitting laser according to an eleventh aspect of the present invention is the surface-emitting laser according to the first aspect, wherein the oscillation wavelength of the surface-emitting laser light is a wavelength within a range of 510 to 550 nm. Is.
Thereby, a green surface emitting laser with high reliability can be realized.

A surface-emitting laser according to a twelfth aspect of the present invention is the surface-emitting laser according to the sixth aspect, wherein a non-linear optical material that converts the wavelength of the laser light disposed between the external mirror and the active layer is used. It is characterized by having.
As a result, a high-power laser light source that can generate short-wavelength light can be realized.

  The surface-emitting laser according to claim 13 of the present invention is the surface-emitting laser according to claim 1, wherein the semiconductor layer stack includes the active layer formed by stacking a plurality of semiconductor layers on the surface of the semiconductor substrate. The semiconductor substrate is formed by etching a part of the back surface to the vicinity of the surface of the active layer to form a recess.

  As a result, the absorption of laser light in the semiconductor substrate can be reduced, and high output can be achieved.

  According to a fourteenth aspect of the present invention, there is provided a semiconductor laser device comprising: a semiconductor laser that outputs a laser beam; and a wavelength conversion element that converts the wavelength of the laser beam from the semiconductor laser. Is a surface emitting laser according to claim 1.

  As a result, it is possible to realize a high-power semiconductor laser device capable of generating short-wavelength light, in which laser light from the surface-emitting laser is wavelength-converted and output.

  A laser module according to claim 15 of the present invention is a laser module in which a plurality of semiconductor lasers are integrated in one package, and each of the semiconductor lasers is a surface emitting laser according to claim 1. It is characterized by.

  Thereby, a multi-wavelength light source such as an RGB light source can be realized, and an ultra-compact laser irradiation apparatus can be realized by using such a multi-wavelength light source and a condensing optical system.

  The laser module according to a sixteenth aspect of the present invention is the laser module according to the fifteenth aspect, wherein each of the plurality of semiconductor lasers is positioned at a vertex of a regular polygon whose center coincides with the center of the package. It is arrange | positioned so that it may carry out.

  As a result, the package structure can be simplified and the cost can be reduced, and the output and life of the laser module can be increased.

  A laser projection apparatus according to claim 17 of the present invention is a laser projection apparatus comprising: a semiconductor laser that outputs laser light; and a projection optical system that projects the laser light output from the semiconductor laser. The laser is a surface emitting laser according to claim 1.

  As a result, it is possible to realize an ultra-compact laser projection device capable of achieving high output, in which the lateral mode stability at high output is greatly increased.

  The laser projection device according to an eighteenth aspect of the present invention is the laser projection device according to the seventeenth aspect, wherein the surface emitting laser emits a laser beam having a longitudinal mode spectrum of multimode. is there.

  Thereby, the coherency of the laser light is reduced, and speckle noise can be reduced.

  According to a nineteenth aspect of the present invention, there is provided the laser projection device according to the seventeenth aspect, wherein the surface emitting laser emits a laser beam having a substantial width of a longitudinal mode spectrum of 1 nm or more. It is a feature.

  Thereby, it is possible to realize a laser projection apparatus in which speckle noise is greatly reduced.

  A surface-emitting laser according to claim 20 of the present invention is a surface-emitting laser that performs surface emission of a laser beam, an active layer formed on a semiconductor substrate, and a pair of electrodes that inject carriers into the active layer; One of the pair of electrodes is divided into a plurality of electrode portions, and a laser drive voltage on which a high frequency component is superimposed is applied to at least one of the plurality of electrode portions. It is what.

  This makes it possible to adjust the density of carriers injected from each electrode portion into the active layer by the drive voltage applied to each electrode portion, and the active voltage can be obtained regardless of the light intensity distribution in the surface emitting laser active layer. It is possible to realize a surface emitting laser having excellent high output characteristics in which the carrier density in the layer is made uniform and the transverse mode stability at high output is greatly increased. In addition, since a laser drive voltage with a high frequency component superimposed on the electrode is applied, the laser oscillation state changes and the temporal coherency of the laser light is reduced, thereby reducing noise caused by the return light. Can do.

  The surface-emitting laser according to claim 21 of the present invention is the surface-emitting laser according to claim 20, wherein the plurality of divided electrode portions are arranged substantially uniformly around the emission center of the laser beam. It is characterized by that.

  Thus, by applying the same level of driving voltage to the electrode portions having the same distance from the emission center, it is possible to easily make the carrier density uniform in the active layers having different light intensity distributions.

  The surface emitting laser according to claim 22 of the present invention is the surface emitting laser according to claim 20, wherein the current density from the electrode portions to the active layer is closer to the emission center of the active layer. It is characterized in that it is performed so as to be higher.

  Thereby, the density distribution of the injected carrier suitable for the light intensity distribution can be realized in the active layer having the light intensity distribution in which the peak of the light intensity is located at the emission center.

  The surface emitting laser according to claim 23 of the present invention is the surface emitting laser according to claim 20, wherein a modulated laser driving voltage is applied to at least one of the plurality of electrode portions. It is.

  As a result, speckle noise can be suppressed by reducing coherency while alleviating the chirping phenomenon in which the oscillation wavelength varies.

  A surface-emitting laser according to a twenty-fourth aspect of the present invention is the surface-emitting laser according to the twentieth aspect, wherein each semiconductor laser portion formed by each electrode portion is driven with a different injection current. is there.

  As a result, in the active layer corresponding to each semiconductor laser, it becomes possible to realize a carrier injection density corresponding to the light intensity distribution, and to increase the output of the surface emitting laser while suppressing spatial hole burning. it can.

  The surface-emitting laser according to claim 25 of the present invention is the surface-emitting laser according to claim 20, wherein the semiconductor layer stack includes the active layer and is formed by stacking a plurality of semiconductor layers on the surface of the semiconductor substrate. The semiconductor substrate is formed by etching a part of the back surface to the vicinity of the surface of the active layer to form a recess.

  As a result, the absorption of laser light in the semiconductor substrate can be reduced, and high output can be achieved.

  According to the present invention, in the surface-emitting laser, the density distribution of carriers injected into the active layer of the surface-emitting laser is made to be a distribution according to the light power distribution in the active layer. It is possible to avoid the occurrence of hole burning due to an increase in current density in the region corresponding to the portion, and to greatly increase the transverse mode stability at the time of high output, thereby improving the high output characteristics.

  As a result, a high-power surface-emitting laser capable of performing laser oscillation in a stable transverse mode and efficiently injecting current into the active layer, and such a high-power surface-emitting laser as a light source. The laser projection apparatus used can be obtained.

  Embodiments according to the present invention will be described below in detail with reference to the drawings.

(Embodiment 1)
1A and 1B are diagrams for explaining a surface emitting laser according to Embodiment 1 of the present invention. FIG. 1A shows a sectional structure thereof, FIG. 1B shows a shape of a lower electrode thereof, and FIG. c) shows the light intensity distribution in the light emitting region of the active layer. In FIG. 1, the same reference numerals as those in FIG. 14 are the same as those in the conventional surface emitting laser.

  The surface emitting laser 100a according to the first embodiment is formed in a semiconductor layer stack 110 in which an active layer 3 and a reflective layer 4 are stacked on the surface of a semiconductor substrate 2a, and in a predetermined region on the reflective layer 4. A lower electrode 6 and a planar ring-shaped upper electrode 5 formed on the back side of the semiconductor substrate 2a are provided.

  Here, the semiconductor substrate is made of a nitrogen compound mainly containing GaN, and the active layer 3 is made of a nitride semiconductor mainly containing GaN. The reflective layer 4 is a dispersive black reflective layer (hereinafter referred to as a DBR layer) formed by alternately laminating materials 4 a and 4 b having different refractive indexes on the active layer 3.

  In the surface emitting laser 100a according to the first embodiment, the lower electrode 6 has a star shape obtained by cutting out a regular octagonal region of an isosceles triangle having each side as a base. Therefore, the surface density of the portion where the lower electrode 6 and the DBR layer 4 are in contact is large at the central portion of the lower electrode 6 and is small at the peripheral portion of the lower electrode 6. Here, the lower electrode 6 is arranged so that the center thereof coincides with the center of the ring-shaped upper electrode 5, and the maximum width is larger than the inner diameter of the ring-shaped upper electrode 5, and the outer diameter is larger than the outer diameter. It is a small one. Further, a portion of the semiconductor substrate 2a exposed to the inside of the upper electrode 5 is etched to the vicinity of the surface of the active layer 3, and is thinner than the other portions.

  The surface-emitting laser 100a according to the first embodiment has an external mirror 1 disposed above the ring-shaped upper electrode 5, and an active layer is formed by the external mirror 1 and the DBR layer 4. 3 is configured to amplify the light generated in 3 so that laser oscillation occurs. Here, the substrate side surface of the external mirror 1 has a concave shape.

Next, the function and effect will be described.
First, the laser oscillation operation of the surface emitting laser 100a according to the first embodiment will be briefly described.

  In the surface emitting laser 100 a, when a laser driving voltage is applied between the upper electrode 5 and the lower electrode 6, a current is injected into the active layer 3. When the magnitude of the injection current becomes a certain value, that is, larger than the laser oscillation threshold, laser oscillation occurs in the resonator, and the laser beam 8 is emitted outside through the external mirror 1. At this time, the laser beam 8 is surface-emitted, and the emission direction of the laser beam is perpendicular to the surface of the semiconductor substrate 2a.

  Next, the characteristics of the surface emitting laser according to the first embodiment will be described in comparison with the conventional one.

  In the conventional surface emitting laser, the lower electrode has an electrode structure in which a circular conductor layer is formed on the DBR layer 4. For this reason, if the injection current is increased in order to obtain high power, the current density at the periphery of the electrode increases, and due to the occurrence of hole burning, the gain decreases or the transverse mode becomes unstable, An increase in injected current causes a decrease in output and unstable operation. On the other hand, in the vicinity of the center of the electrode, a shortage of injected carriers occurs due to an increase in light power density. As described above, in the conventional surface emitting laser, when the output is high, the transverse mode becomes multi-level and the mode becomes unstable, and it is difficult to realize a stable transverse mode.

  On the other hand, in the surface emitting laser 100a according to the first embodiment, the shape of the lower electrode 6 is a star shape shown in FIG. It becomes possible to approximate the light intensity distribution in the active layer.

  That is, as shown in FIG. 1C, the light intensity distribution in the active layer 3 has the highest light intensity Lp at the emission center and decreases toward the periphery, and the light intensity distribution is close to a Gaussian distribution. It has become. Therefore, by making the planar shape of the lower electrode 6 into the star shape shown in FIG. 1B, the surface density of the portion where the lower electrode 6 and the DBR layer 4 are in contact with each other is reduced from the center of the lower electrode to the periphery. Decreases over time. In other words, the density of current (carrier) injected from the lower electrode 6 into the active layer 3 is maximized at the central portion of the lower electrode 6 and decreases as it goes to the peripheral portion, as shown in FIG. It becomes. As a result, the density distribution of the current injected into the active layer 3 corresponds to the light intensity distribution in the active layer 3, and the lateral mode stability at high output is greatly improved. A surface emitting laser having output characteristics can be realized.

  Conventionally, a surface emitting laser that can adjust the distribution of injected carrier density as a structure in which an electrode is divided into a plurality of parts has already been proposed. However, when the electrode of the surface emitting laser is divided, there is a problem that the resistance separation layer located at the portion where the electrode is divided causes a loss in the current injected into the active layer and the efficiency is lowered. In addition, in such a plurality of divided electrodes, the injected carrier density distribution can be changed only discretely, so that the density distribution of the injected carrier and the light intensity distribution are not sufficiently matched. Furthermore, since a laser driving voltage is applied to the divided electrodes so that current is injected into the active layer from each electrode at a different current density, the laser driving circuit becomes complicated. There was a problem.

  On the other hand, in the surface emitting laser 100a of the first embodiment, the planar shape of the lower electrode 6 is such that the surface density of the portion where the lower electrode 6 and the DBR layer 4 are in contact is the central portion of the lower electrode 6. Since it is star-shaped so as to be large and small in the peripheral portion of the lower electrode 6, the injected carrier density distribution can be continuously changed. Further, in the conventional surface emitting laser, resistance separation for separating the electrodes is possible. Since no layer is required, there is little injection current loss and efficient laser oscillation is possible.

  As described above, the first embodiment has the active layer 3 formed on the semiconductor substrate 2a and the pair of upper electrode 5 and lower electrode 6 for injecting carriers into the active layer 3, and the lower electrode 6 The star shape is such that current injection from the lower electrode 6 to the active layer 3 is performed at a high current density in the central portion of the lower electrode 6 and at a low current density in the peripheral portion. Therefore, the density distribution of carriers injected into the active layer 3 of the surface emitting laser can be set to a distribution according to the light power distribution in the active layer. This prevents the occurrence of hole burning due to an increase in current density in the region of the active layer corresponding to the periphery of the electrode, resulting in excellent high output characteristics that greatly increased lateral mode stability at high output. A surface emitting laser having the same can be realized.

  In the first embodiment, the region of the semiconductor substrate 2a facing the lower electrode 6 is thinned by etching to the vicinity of the surface of the active layer 3, so that the region of the active layer 3 faces the lower electrode 6. It is possible to reduce the absorption of the laser light generated in the portion by the semiconductor substrate 2a, and it is possible to efficiently extract the laser light from the back side of the semiconductor substrate 2a.

  Further, in the structure in which the laser light is extracted from the back surface side of the semiconductor substrate 2a in this way, a metal electrode layer having high thermal conductivity can be formed on the surface of the DBR layer 4 on the active layer 3 at a position close to the active layer. it can. Furthermore, the surface emitting laser can efficiently escape the heat generated in the active layer 3 by arranging the metal electrode layer as described above in close contact with the heat sink. As a result, the temperature rise in the active layer 3 can be suppressed, and the output of the surface emitting laser can be further increased.

  Further, in the first embodiment, the resonator of the surface emitting laser 100a is configured by the DBR layer 4 formed on the semiconductor substrate 2a and the external mirror 1 disposed away from the semiconductor substrate 2a. A sufficient resonator length can be secured. Thereby, the stability of the transverse mode of the resonator can be increased, and the light intensity distribution in the active layer 3 near the lower electrode 6 can be increased.

  For example, the range of the light intensity distribution in the active layer is substantially proportional to the resonator length, and the resonator length can be increased 10 times or more by using the external mirror 1, thereby enabling an effective active layer. The area can be increased. As a result, the surface emitting laser can dramatically improve the high output characteristics, which increase in proportion to the effective active layer area.

  In addition, in a surface emitting laser having a resonator having an external active mirror and having a large effective active layer area, the problem of the consistency between the light intensity distribution and the injected carrier distribution in the active layer 3 becomes significant. In Embodiment 1, since the planar shape of the lower electrode 6 of the surface emitting laser is a star shape, the inconsistency problem between the carrier density distribution and the light intensity distribution in the external mirror type surface emitting laser is solved, and the surface emitting Lasers have greatly improved high power characteristics.

  Further, in the surface emitting laser of the first embodiment, a self-excited oscillation state using supersaturated absorption, that is, a laser beam is emitted in a pulsed form as an output even though a current applied to the semiconductor laser is a direct current. The speckle noise can be reduced by changing the oscillation wavelength according to the oscillation state.

  That is, in the surface emitting laser of the first embodiment, the planar shape of the lower electrode 6 is such that current injection from the lower electrode 6 to the active layer 3 is performed at a high current density in the central portion of the lower electrode 6. Since the peripheral portion is shaped so as to be performed at a low current density, by providing a saturable absorber in a portion corresponding to the periphery of the lower electrode 6 in the active layer so as to reduce the injection current density, In high-power surface emitting lasers, speckle noise can be reduced by self-excited oscillation using supersaturated absorption.

  In the first embodiment, the planar shape of the lower electrode 6 is such that the surface density of the portion where the lower electrode 6 and the DBR layer 4 are in contact is continuously from the central portion of the lower electrode 6 to the peripheral portion thereof. Although the star shape is changed so as to change, the structure of the lower electrode 6 is not limited to such a planar star shape.

For example, the lower electrode 6 may be formed with a plurality of fine holes so that the surface density of the portion where the lower electrode 6 is in contact with the DBR layer 4 is different between the central portion of the lower electrode 6 and its peripheral portion.
FIG. 2 is a diagram for explaining an example of the structure of the lower electrode in which such fine holes are formed.

  A lower electrode 6a shown in FIG. 2A is obtained by forming a plurality of fine holes in a single electrode layer constituting the electrode. In the lower electrode 6a, the diameter of the minute hole 7a formed in the center is smaller than the diameter of the minute hole 7c formed in the peripheral part. Further, the diameter of the fine hole 7b formed in the intermediate part between the center part and the peripheral part of the lower electrode 6a is smaller than the diameter of the fine hole 7a formed in the central part, and the diameter of the fine hole 7c formed in the peripheral part. Greater than.

  The lower electrode 6a in which a plurality of fine holes are formed in this manner is similar to the lower electrode 6 of the first embodiment, the closer the surface density of the portion where the lower electrode 6a and the DBR layer 4 are in contact is closer to the center. As a result, the density distribution of carriers injected into the active layer of the surface emitting laser can be made to be a distribution corresponding to the power distribution of light in the active layer.

  Further, the lower electrode 6b shown in FIG. 2 (b) is formed by forming a plurality of fine holes in a single electrode layer constituting the electrode, like the lower electrode 6a shown in FIG. 2 (a). In the lower electrode 6b, the arrangement density of the fine holes 7d increases as it is closer to the periphery.

  The lower electrode 6b in which a plurality of fine holes are formed in this manner is similar to the lower electrode 6 of the first embodiment, the closer the surface density of the portion where the lower electrode 6b and the DBR layer 4 are in contact is closer to the center thereof. As a result, the density distribution of carriers injected into the active layer of the surface emitting laser can be made to be a distribution corresponding to the power distribution of light in the active layer.

  In the lower electrode 6a shown in FIG. 2A or the lower electrode 6b shown in FIG. 2B, a metal layer constituting the lower electrode is easily formed by selective etching using a mask. Can do.

  In addition, the lower electrode having a plurality of such fine holes can be formed so as to spread over the entire region where the hole can be arranged, thereby improving the heat dissipation effect to the heat sink.

In the first embodiment, the density of the current injected into the active layer is adjusted to match the light intensity distribution in the active layer by the planar shape of the lower electrode. The density distribution of the current injected into the first electrode may be adjusted by, for example, disposing a current stop layer partially between the lower electrode 600 and the DBR layer 4 in a conventional surface emitting laser.
FIG. 3 is a diagram for explaining a specific example of such a current stop layer.

  The current stop layer shown in FIG. 3A is composed of the insulating layer 11 formed between the lower electrode 600 and the DBR layer 4 and having a plurality of holes.

  A large-diameter hole 11a is formed in the insulating layer 11 at a portion corresponding to the center portion of the lower electrode 600, and a plurality of medium-diameter holes 11b having a smaller diameter are formed around the large-diameter hole 11a. In addition, a plurality of small-diameter holes 11c having a smaller diameter are formed outside the medium-diameter hole 11b.

  By disposing the insulating film 11 in which a plurality of holes are formed in this manner between the lower electrode 600 and the DBR layer 4, the lower electrode 600 and the DBR layer 4 are brought into contact with each other as in the first embodiment. The closer the surface density of the portion is to the central portion, the larger the density, so that the density distribution of carriers injected into the active layer of the surface emitting laser can be made to be a distribution corresponding to the light power distribution in the active layer.

  The current stop layer shown in FIG. 3B is formed of an insulating layer 12 formed between the lower electrode 600 and the DBR layer 4 and having a plurality of holes.

  A large-diameter hole 12a is formed in the insulating layer 12 at a portion corresponding to the center portion of the lower electrode, and a plurality of small-diameter holes 12b having a small diameter are formed outside the large-diameter hole 12a. As the distance from the center of the lower electrode 600 increases, the density of the holes 12b decreases.

  By disposing the insulating film 12 in which a plurality of holes are formed in this manner between the lower electrode 600 and the DBR layer 4, the lower electrode 600 and the DBR layer 4 are brought into contact with each other as in the first embodiment. The closer the surface density of the portion is to the central portion, the higher the density, so that the density distribution of carriers injected into the active layer of the surface emitting laser can be made to be a distribution corresponding to the light power distribution in the active layer.

  In addition, as shown in FIGS. 3A and 3B, the electrode structure in which the current stop layer is disposed between the lower electrode and the DBR layer is easy to form the lower electrode. Since the area of the lower electrode can be increased, the contact area where the lower electrode is joined to an external heat sink via solder is also increased. Therefore, the electrode structure using the current stop layer shown in FIG. 3A or FIG. 3B is excellent in heat dissipation effect and superior in high output.

  Further, the electrode structure shown in FIG. 3A or 3B may have a resistance layer having an in-plane distribution of resistance values instead of the current stop layer.

  In this case, the resistance distribution of the resistance layer in the electrode structure is such that the resistance value decreases as the distance from the center of the lower electrode increases. As a result, the density distribution of carriers injected into the active layer of the surface emitting laser can be made to be a distribution corresponding to the light power distribution in the active layer.

  Furthermore, the electrode structure that connects the lower electrode and the DBR layer is not limited to the one having the current stop layer and the resistance layer, and the lower electrode itself may have an in-plane distribution of resistance values. Good. In this case, the resistance distribution of the lower electrode has a resistance value that decreases as the distance from the center increases. As a result, the density distribution of carriers injected into the active layer of the surface emitting laser can be made to be a distribution corresponding to the light power distribution in the active layer.

  In the first embodiment, the semiconductor substrate constituting the surface emitting laser is made of a semiconductor made of a nitrogen compound containing GaN as a main component, but the semiconductor substrate of the surface emitting laser is, for example, an SiC substrate or the like. The III-V nitride semiconductor material may be epitaxially grown thereon.

  Further, the surface emitting laser of the present invention is not limited to the one made of the above-described III-V group nitride semiconductor material. For example, the constituent material of the surface emitting laser may be an AlGaAs-based, AlGaInP-based semiconductor material, or a ZnSe-based semiconductor material. Even when such a semiconductor material is used, the high-frequency laser oscillation in a stable fundamental transverse mode is possible. An output surface emitting laser can be realized. In particular, when an AlGaInP-based semiconductor material is formed on a GaAs substrate whose substrate plane orientation is inclined from (100) to the [0-11] or [011] direction, band gap fluctuation due to crystal ordering does not occur. By using an AlGaInP-based semiconductor material, a surface emitting laser capable of stable high output operation can be realized.

  In the first embodiment, a recess 9 is formed by etching a region facing the lower electrode 6 of the semiconductor substrate 2a from the back surface side to the vicinity of the active layer 3 on the substrate surface side. Although the ring-shaped upper electrode 5 is formed on the back surface of the substrate so as to surround, the upper electrode 5 is not limited to the ring-shaped one formed on the back surface side of the semiconductor substrate 2a, but is formed on the bottom surface of the recess 9, for example. A transparent electrode may be used. When such a transparent electrode is used, the active layer and the upper electrode are brought closer to each other, so that the loss of the injection current into the active layer can be more effectively reduced.

  In the first embodiment, the recess 9 is formed by etching the region facing the lower electrode 6 of the semiconductor substrate 2a from the back surface side to the vicinity of the active layer 3 on the substrate surface side. When a material having a high conductivity and transparent to the laser light is used as the material for the semiconductor substrate of the surface emitting laser, the concave portion 9 does not need to be formed.

  In the first embodiment, as a surface emitting laser, a resonator includes a DBR layer 4 that is one of a plurality of semiconductor layers stacked on the semiconductor substrate 2a, and an external mirror that is disposed apart from the semiconductor substrate 2a. However, the surface-emitting laser may be a normal thin-film surface-emitting laser in which a resonator is formed by a semiconductor layer stacked on a semiconductor substrate. As in the first embodiment, the planar shape of the lower electrode 6 is such that current injection from the lower electrode 6 to the active layer has a high current density in the central portion of the lower electrode and a low current in the peripheral portion. By adopting a shape that is performed at a high density, it is possible to dramatically improve the high output characteristics.

  In the first embodiment, the surface emitting laser is one laser element having one surface emitting portion, but the surface emitting laser that is one laser element is a multi-beam type having a plurality of surface emitting portions. The surface emitting laser may be used. In this case, the saturation of the gain in each surface emitting portion is achieved by setting the density distribution of carriers injected into the active layer in each surface emitting portion of the surface emitting laser according to the light power distribution in the active layer. Can be mitigated, and a semiconductor laser having a higher output than the surface emission of laser light can be realized.

(Embodiment 2)
4A and 4B are diagrams for explaining a surface emitting laser according to Embodiment 2 of the present invention. FIG. 4A shows the cross-sectional structure, FIG. 4B shows the shape of the lower electrode, and FIG. c) shows the light intensity distribution in the light emitting region of the active layer. In FIG. 4, the same reference numerals as those in FIG. 1 are the same as those in the surface emitting laser of the first embodiment.

  The surface-emitting laser 100b according to the second embodiment includes a lower electrode 60 divided into two in place of the star-shaped lower electrode 6 in the surface-emitting laser 100a according to the first embodiment. In the surface emitting laser 100b, the surface of the recess 9 formed on the back surface side of the semiconductor substrate 2a is provided with a non-reflective coating so as to reduce the light loss in the resonator.

  Here, as shown in FIG. 4B, the lower electrode 60 includes a circular inner electrode portion 60a located at the center thereof and a ring-shaped outer electrode portion arranged so as to surround the inner electrode portion 60a. 60b. Further, a portion of the lower electrode 60 divided into two parts between the outer electrode portion 60b and the inner electrode portion 60a is a resistance separating portion 61 having a high resistance value. Thus, by making the lower electrode 60 into two parts, the density distribution of the current injected into the active layer 3 can be adjusted according to the light intensity distribution in the active layer 3.

  That is, as shown in FIG. 4C, the light intensity distribution in the active layer 3 has the highest light intensity Cd2 at the center of the light emitting region, that is, at the center of the region of the active layer 3 facing the lower electrode. It is close to a Gaussian distribution that decreases with increasing distance from the center. Therefore, in the surface emitting laser 100b of the second embodiment, the laser driving voltage applied to the inner electrode portion 60a is set to the outer side so that the density distribution of the current injected into the active layer 3 corresponds to the light intensity distribution. It is higher than the laser drive voltage applied to the electrode part 60b. In the surface emitting laser 100b, the laser driving voltage applied to the outer electrode portion 60b is obtained by superimposing a high frequency component on a direct current component so that the coherence of the generated laser light is reduced.

Next, the function and effect will be described.
The basic laser oscillation operation of the surface emitting laser 100b according to the second embodiment is performed in the same manner as the surface emitting laser 100a according to the first embodiment.

In the second embodiment, since the laser driving voltage on which the high frequency component is superimposed is applied to the outer electrode portion 60b of the divided lower electrode 60, the active electrode 3 faces the outer electrode portion 60b. The carrier density fluctuates in the part where For this reason, the laser oscillation state in the entire resonator varies, and temporal coherence is reduced.
Next, the characteristics of the surface emitting laser according to the second embodiment will be described in comparison with the conventional one.

  In the conventional surface-emitting laser, as described above, the lower electrode has a single electrode structure, so that at the time of high output, the lateral mode becomes multi-mode and the mode becomes unstable, thereby realizing a stable lateral mode. It was difficult.

  On the other hand, in the surface emitting laser 100b of the second embodiment, the lower electrode 60 is divided into two as shown in FIG. 4B, so that the density distribution of carriers injected into the active layer can be obtained. It is possible to approximate the light intensity distribution in the active layer, thereby realizing a surface emitting laser having excellent high output characteristics, which greatly improves the transverse mode stability at high output. .

  Further, in the second embodiment, the resonator of the surface emitting laser 100a is constituted by the DBR layer 4 formed on the semiconductor substrate 2a and the external mirror 1 arranged away from the semiconductor substrate 2a. Similar to the first embodiment, a sufficient resonator length can be secured. Thereby, the stability of the transverse mode of the resonator can be increased, and the light distribution in the active layer 3 in the vicinity of the lower electrode 60 can be increased.

  In addition, in a surface emitting laser having a resonator having an external active mirror and having a large effective active layer area, the problem of the consistency between the light intensity distribution and the injected carrier distribution in the active layer 3 becomes significant. In Embodiment 2, since the lower electrode of the surface emitting laser has a two-part structure, the problem of mismatch between the carrier density distribution and the light intensity distribution in the external mirror type surface emitting laser is solved, and the surface emitting laser has a high output. The characteristics are greatly improved.

  Further, even in a surface emitting laser in which the lower electrode is divided into a plurality of parts, if the effective active layer area is small, it is difficult to form the injected carrier density distribution by dividing the lower electrode, and the resistance separation layer portion between the separated electrodes In the second embodiment, however, the active layer area is sufficiently large by using the external mirror 1 as described above. For this reason, the injection current caused by the resistance separation layer is used. Since the problem of loss is almost negligible, the two-part structure of the lower electrode is effective.

  Further, in the second embodiment, the characteristics are greatly improved by changing the characteristics of the current injected into each divided electrode part. In particular, with conventional surface emitting lasers, it has been difficult to drive stably, modulate laser light, or superimpose a high-frequency component on the laser driving current when used with a large output of 100 mW or more. These problems are also solved in the surface emitting laser of the second embodiment.

  Here, a mechanism for preventing the generation of noise due to the return light in the surface emitting laser according to the second embodiment will be described.

  The return light noise is a phenomenon in which the noise is greatly increased by the light emitted from the semiconductor laser returning to the active layer. In order to prevent this, a method of reducing the coherence of light is usually employed. As one of them, there is a method of superimposing an RF signal of about several hundred MHz on the drive current. However, the conventional high-power semiconductor laser has a problem in that the required RF power is greatly increased due to an increase in driving current. Such an increase in the RF power greatly increases the cost of the entire system due to the increase in power consumption and the necessity of measures for heat dissipation and radiation.

  The surface emitting laser 100b according to the second embodiment solves the problem of high-frequency superposition in such a high-power laser.

  That is, the high frequency superposition is to change the state of the carrier density of the semiconductor laser, thereby changing the light oscillation state with time and reducing temporal coherence. Therefore, the rate of change with respect to the density of carriers injected into the active layer is important.

  In conventional surface emitting lasers with a single electrode structure, the injected current is dispersed throughout the electrode. Therefore, in order to change the injected carrier density greatly, the ratio of the current changed at a high frequency is increased with respect to the injected current. Therefore, the RF amplitude of the high-frequency component superimposed on the laser drive current is large.

  On the other hand, in the surface emitting laser 100b according to the second embodiment, the lower electrode 60 is divided into a plurality of electrode portions, and RF is superimposed on only some of the electrode portions. In the surface emitting laser 100b having such a configuration, since the lower electrode is divided into a plurality of parts, the injection current due to each electrode portion is significantly lower than the injection current due to the entire lower electrode. That is, the RF amplitude when the RF signal is superimposed on a part of the plurality of electrode portions obtained by dividing the lower electrode is a fraction of the RF amplitude when the RF signal is superimposed on a single lower electrode. This can greatly reduce the power of high frequency superposition. In addition, even when an RF signal is superimposed on a part of the electrode part, since the fluctuation of the injected carrier density by the electrode part can be sufficiently obtained, the oscillation state of the entire resonator changes and the temporal coherence can be lowered. it can.

  Furthermore, in the surface emitting laser 100b of the second embodiment, as shown in the light intensity distribution diagram of FIG. 4C, when a high output is obtained, a large current is applied to the electrode unit 60a located near the center of the light emitting region. However, only a small current corresponding to the power density of the light is required in the peripheral electrode part 60b far from the center of the light emitting region. For this reason, by superimposing the RF signal on the laser drive current supplied to the electrode part located near the periphery of the light emitting region, the coherence can be reduced efficiently with low RF power, resulting in the miniaturization of the system. Thus, cost reduction and power consumption can be reduced.

  In addition, the structure of the second embodiment in which the electrodes are divided is particularly effective for a GaN laser, and will be briefly described below.

  When a semiconductor laser based on a GaN substrate has a large relaxation oscillation and high frequency superposition is performed, spike noise is generated. This is a phenomenon in which when the current injected into the semiconductor laser is modulated with a high-frequency signal, the output light waveform changes in a spike shape due to relaxation oscillation, and a pulse output many times higher than the modulation degree is generated. In an optical disk system using a GaN laser, a high-frequency signal is superimposed on a laser drive current in order to prevent laser noise from increasing due to return light during reproduction of the optical disk. However, since the GaN laser produces a spike-like output with a high spire value even when the average power during reproduction is low, this causes the problem of degradation of the reproduction light that deteriorates the data recorded during reproduction. appear.

  On the other hand, in the configuration in which the electrode is divided into a plurality of parts and a high frequency signal is superimposed on a part of the electrode part, the spire output spire value is greatly reduced to less than half while the laser return light noise is reduced. I understood that I could do it.

  Therefore, the surface emitting laser 100b according to the second embodiment in which the lower electrode is divided into a plurality of parts is preferable for application to an optical disk device or the like.

  In addition, even a laser other than a GaN-based laser, for example, a semiconductor laser using an AlGaAs-based semiconductor material or an AlGaInP-based semiconductor material, can efficiently superimpose a high-frequency signal on a laser drive current as a structure in which electrodes are divided. Is possible.

  Furthermore, the configuration of the second embodiment in which the lower electrode is divided into a plurality of parts plays an effective role even when the output of the surface emitting laser is modulated.

  Currently, when modulating the output of a semiconductor laser, the entire laser drive current is modulated. However, when the entire driving current of the semiconductor laser is changed, a chirping phenomenon in which the oscillation wavelength varies due to a change in the temperature of the semiconductor laser due to an increase in power consumption occurs. For example, when recording on a medium such as an optical disk, recording is performed while modulating the light source light. At this time, if the wavelength of the light source light fluctuates due to chirping, the size of the focused spot changes due to the influence of chromatic aberration. To do. This phenomenon is particularly remarkable in a short wavelength region where the dispersion characteristics of the optical system are remarkable.

  The surface emitting laser 100b according to the second embodiment is effective in suppressing such a chirping phenomenon, and has a structure in which the lower electrode is divided into two electrode portions, and the current injected into one electrode portion. By modulating, the variation of the injection current in the entire laser accompanying the modulation of the injection current is reduced, and chirping can be suppressed to a low level.

  As described above, in the second embodiment, the lower electrode 60 is divided into the inner electrode portion 60a and the outer electrode portion 60b, and the laser driving voltage in which the high frequency signal is superimposed on the outer electrode portion far from the center of the light emitting region. Therefore, the density distribution of carriers injected into the active layer of the surface emitting laser can be made to be a distribution according to the light intensity distribution in the active layer.

  Specifically, as compared with a conventional surface emitting laser having a single-structure electrode, it is possible to inject more carriers into the emission center portion even at the same injection current value, and an electrode far from the emission center. The phenomenon in which the density of carriers injected from the portion into the active layer becomes extremely high can be alleviated. As a result, by improving the slope efficiency, it is possible to reduce the injected carrier density and improve the saturation level of the optical output.

  Furthermore, the effect of increasing the light output by the electrode structure divided into a plurality of in the surface emitting laser of the second embodiment is particularly effective in a gallium nitride surface emitting laser having a high threshold carrier density and a high differential gain. is there.

  In the second embodiment, the lower electrode 60 has a two-divided structure, but the lower electrode may have a more finely divided structure. At this time, the plurality of divided electrode portions are arranged substantially uniformly around the emission center of the laser beam. Thereby, the carrier density in the active layers having different light intensity distributions can be made uniform easily, and more stable single transverse mode operation can be realized at high output.

  Further, the surface emitting laser according to the second embodiment is not limited to the one made of the above-described III-V group nitride semiconductor material. For example, the constituent material of the surface emitting laser according to the second embodiment may be an AlGaAs-based, AlGaInP-based semiconductor material, or a ZnSe-based semiconductor material. Even when such a semiconductor material is used, a plurality of lower electrodes are provided. With the divided structure, it is possible to realize a high-power semiconductor laser that performs laser oscillation in a stable fundamental transverse mode.

  In the first embodiment or the second embodiment, the single surface emitting laser formed on the semiconductor substrate has been described. However, the surface emitting laser 100a according to the first embodiment or the embodiment is formed on one semiconductor substrate. A plurality of the surface emitting lasers 100b of the second embodiment may be formed.

  FIG. 5 is a diagram showing a specific example of a semiconductor laser device in which a plurality of surface emitting lasers are formed on one semiconductor substrate. FIG. 5 (a) shows the shape of the lower electrode, and FIG. Vb-Vb sectional drawing is shown.

  As shown in FIG. 5A, the semiconductor laser device 120 is formed by forming a plurality of surface-emitting lasers 120b identical to the surface-emitting laser of the second embodiment on one semiconductor substrate 22.

  Specifically, as shown in FIG. 5B, an active layer 23 and a DBR layer 24 are stacked on the surface of the semiconductor substrate 22. A separation groove 62 a that reaches the inside of the substrate from the surface side of the DBR layer 24 is formed on the surface side of the semiconductor substrate 22, and an insulating material is embedded in the separation groove to form a resistance separation region 62. A plurality of the separation grooves 62a are formed in the vertical direction and the horizontal direction, and the lower electrode 26 divided into two is arranged on the region surrounded by the separation grooves 62a, like the lower electrode in the second embodiment. Yes.

  Further, a ring-shaped upper electrode 25 is formed on the other surface of the semiconductor substrate 22 so as to face the lower electrode 26, and a concave portion 29 by etching is formed on an inner portion of the upper electrode 25 of the substrate 22. Is formed. Further, an external mirror 21 is disposed above the upper electrode 25.

  Thus, by forming a plurality of surface emitting lasers 120b in one substrate and separating the adjacent surface emitting lasers 120b by the resistance isolation region 62, it becomes possible to achieve high output, and the adjacent surfaces Mutual influence between the light emitting lasers 120 b can be avoided by the resistance isolation region 62.

(Embodiment 3)
FIG. 6 is a schematic configuration diagram illustrating a laser projection apparatus according to Embodiment 3 of the present invention.

  The laser projection device 130 according to the third embodiment includes a laser light source 131, a lens 132 that collimates laser light emitted from the laser light source 131, and a spatial modulator 133 that spatially modulates the collimated laser light. And a projection lens 134 that projects the modulated laser light onto the screen 135. In the laser projection device 130 according to the third embodiment, the same laser light source as the surface emitting laser 100b according to the second embodiment in which the lower electrode is divided into a plurality of parts is used. In the surface-emitting laser that is the laser light source of the third embodiment, the current injected from the partial electrode portion of the lower electrode into the active layer of the lower electrode is modulated, and further, the plurality of electrodes The RF signal is superimposed on the current injected into a part of the part. In particular, in the surface emitting laser of this embodiment, high frequency signals having different frequencies are superimposed on the inner electrode portion and the outer electrode portion.

Next, the function and effect will be described.
Hereinafter, first, the configuration of a semiconductor laser applied to a laser display which is a kind of such a laser projection apparatus will be described.

  The laser display is a display device using RGB laser light, and a large output of several hundred mW to several watts or more is required as a laser output.

  Therefore, consider a case where the surface emitting lasers of the first and second embodiments are applied to a laser display which is a kind of the laser projection apparatus of the third embodiment.

The surface emitting lasers of the first and second embodiments have the following features.
The first feature is that high output is easy and stable single transverse mode oscillation can be performed.

  In addition, the second feature is that the beam shape is close to an ideal circle, and therefore, a converging beam for a laser display can be realized with a simple optical system without requiring a shaping optical system. It is. In particular, the surface emitting laser 100b of the second embodiment is capable of performing high-power optical modulation.

  Although it is very effective to apply a surface emitting laser having such output characteristics to a laser display, in order to use it as a light source for a laser display, the following characteristics are required in addition to the above output characteristics. The

  First, wavelength stability is required. In particular, in a red laser, the wavelength change of the visibility is large, so it is necessary to suppress the wavelength change to ± 1 nm or less.

  Moreover, in order to reduce speckle noise, it is important to reduce coherence, and it is necessary to expand the wavelength spectrum width to several nm.

  In the third embodiment, the above two problems, that is, the point of suppressing the wavelength change and the point of expanding the wavelength spectrum width have been solved, and will be described in comparison with the conventional one.

First, wavelength stabilization will be described.
When an image is projected by laser light, it is necessary to modulate the laser output intensity according to the gradation. At this time, the problem is the mode stability and wavelength change as well as the output intensity. That is, in the laser display, it is necessary to modulate the laser light from 100 mW to a value of several mW or less. At this time, the laser wavelength changes with the output intensity. Therefore, in the conventional high-power semiconductor laser, the driving current differs greatly between high output and low output, so that chirping with significantly different oscillation wavelengths occurs due to the difference in laser temperature.

  On the other hand, in the surface emitting laser that is the laser light source of the laser projection device 130 according to the third embodiment, the lower electrode is divided into a plurality of electrode portions as shown in FIG. By modulating the current injected into the substrate, changes in the injected current can be reduced, and stable modulation can be performed with little wavelength fluctuation. Further, in this surface emitting laser, the gradation can be increased by stabilizing the transverse mode.

Next, expansion of the wavelength spectrum width for reducing speckle noise will be described.
Since a laser display light source requires high output characteristics, it is necessary to perform high-frequency superposition while maintaining an average output at 100 mW or more.

  Therefore, in the conventional semiconductor laser, it is necessary to perform high-frequency superimposition while injecting a current of several hundred mA, and a high-power high-frequency circuit for applying a high-frequency signal having a current amplitude of several hundred mA is required. However, since very large power consumption is required, reduction of power consumption and reduction of external radiation are problems.

  In contrast, in the surface emitting laser as the laser light source according to the third embodiment, the RF current can be reduced by superimposing the RF signal on the current injected into a part of the plurality of divided electrode portions. In the portion of the active layer that is away from the center of the light emitting region, the current density can be reduced, thereby reducing the injection current. As a result, the amplitude of the superimposed RF signal that depends on the injected current can be greatly reduced, and the system can be simplified, reduced in size, and reduced in power consumption.

Next, prevention of speckle noise by further reducing coherence will be described.
Since the decrease in coherence is proportional to the expansion of the spectrum width, the speckle noise can be further reduced if the spectrum width is greatly increased. In order to realize this, it is effective to increase the power of the high-frequency current superimposed on the driving current of the semiconductor laser, but the spectral width expansion due to the power increase of the superimposed high-frequency current is about several nm in wavelength. Limited to.

  Therefore, in the surface emitting laser as the laser light source of the third embodiment, high-frequency signals with different frequencies are applied to the divided inner electrode portion and outer electrode portion so that the spectrum width is further expanded.

  For example, if a high frequency signal of 500 MHz is applied to one of the inner electrode portion and the outer electrode portion and a high frequency signal of 400 MHz is applied to the other, the relative disturbance of the oscillation state due to the injected current from each electrode portion increases. The spread of the spectrum width is increased. At this time, although the increase in the spectrum width is frequency-dependent, the amount of increase in the spectrum width can be increased by 1.2 to 1.5 times compared to the case where a high frequency signal is applied to one electrode.

  The split electrode structure of the surface emitting laser according to the second embodiment used in the laser projection device 130 according to the third embodiment is particularly effective for reducing the coherence of high output light of 100 mW or more.

  Further, in the surface emitting laser used in the laser projection apparatus of the third embodiment, it is possible to reduce speckle noise by changing the oscillation wavelength by self-excited oscillation using supersaturated absorption. The self-excited oscillation is an oscillation state in which laser light is emitted in a pulsed manner despite a direct current flowing through the semiconductor laser.

  That is, since self-excited oscillation uses supersaturated absorption, it was difficult to apply it to a high-power semiconductor laser. However, the surface emitting laser used in the laser projection apparatus of Embodiment 3 has a lower electrode that is connected to an inner electrode portion and an outer electrode. Since it has a structure divided into two parts with the electrode part, high output surface emission can be achieved by providing a saturable absorber in the part of the active layer corresponding to the periphery of the lower electrode where the injection current density is reduced. In the laser, speckle noise can be reduced by self-excited oscillation using supersaturated absorption.

  As described above, in the third embodiment, as the laser light source of the laser projection apparatus, a surface emitting laser having a structure in which the lower electrode is divided into the inner electrode portion and the outer electrode portion is used as in the second embodiment. The density of current injected into the layer can be matched to the light intensity distribution in the active layer, and the current density can be reduced in the portion of the active layer away from the center of the light emitting region, The injection current can be reduced.

In the third embodiment, the RF current can be reduced by superimposing the RF signal on the current injected into the active layer from some of the divided electrodes.
As a result, it is possible to realize simplification, miniaturization, and low power consumption of the laser projection apparatus.

(Embodiment 4)
FIG. 7 is a diagram for explaining a surface emitting laser according to Embodiment 4 of the present invention, and shows a cross-sectional structure of the surface emitting laser. In FIG. 7, the same reference numerals as those in FIG. 1 are the same as those in the surface emitting laser according to the first embodiment.

  The surface emitting laser 100d according to the fourth embodiment includes an external mirror 10 having concave surfaces on both sides, instead of the external mirror 1 in the surface emitting laser 100a according to the first embodiment.

Next, the function and effect will be described.
A surface emitting laser has a small divergence angle of emitted light and can be easily coupled to an optical system such as a fiber. However, in order to reduce the size of the bulk optical system using an external lens or the like, the characteristic that the spread angle of the emitted light is small is not preferable. This is because when the emitted light from the surface emitting laser is collimated or condensed by the lens system, the distance required to spread the light to the effective diameter of the lens becomes long.

  On the other hand, as shown in FIG. 7, the surface emitting laser 100d according to the fourth embodiment is configured such that both surfaces of the external mirror 10 are concave and the spread angle of the outgoing light 8 is increased. Therefore, the surface-emitting laser 100d according to the fourth embodiment has a short distance required for the emitted light to spread to the effective diameter of the lens, and is effective for reducing the size of the bulk optical system.

(Embodiment 5)
8A and 8B are diagrams showing an example of a laser module according to Embodiment 5 of the present invention, in which FIG. 8A is a side view and FIG. 8B is a plan view.

  The laser module 150 of the fifth embodiment is useful as a small RGB light source for application to a laser display.

  This laser module 150 is formed by mounting a surface emitting laser on a package, and three surface emitting lasers 101 to 103 are mounted on a base member 151 of the package. The back surface of the base member 151 is a heat radiating surface, and the lead terminals 101a, 102a, and 103a of the surface emitting lasers 101, 102, and 103 are taken out from the back surface side of the base member 151.

  Here, each of the surface emitting lasers 101 to 103 has the same configuration as the surface emitting laser described in any of Embodiments 1 to 4, and the surface emitting laser 101 is a red surface emitting laser or a surface emitting laser. Reference numeral 102 denotes a green surface emitting laser, and the surface emitting laser 103 is a blue surface emitting laser. These three surface-emitting lasers on the base member 151 are arranged at equal intervals on one circumference with the center of the package as the center.

Next, the function and effect will be described.
To realize a small laser display, it is essential to reduce the size of the light source. In order to realize this, it is effective to use the surface emitting laser described in the first to fourth embodiments as a light source.

  Since the surface emitting lasers mentioned in the first to fourth embodiments have an external mirror, the output can be increased. In addition, these surface emitting lasers have an active layer located in the vicinity of the lower electrode, and therefore have excellent heat dissipation characteristics and are advantageous in generating high output. Further, the surface emitting laser has characteristics such as no deterioration of the end face and excellent reliability because the light power density at the end face on the substrate side is low. In particular, the surface emitting laser according to the second embodiment is advantageous in that the high output characteristics can be dramatically improved by the electrode division structure.

  Furthermore, the surface emitting laser is effective for realizing a modularized multi-wavelength integrated light source. Specifically, the surface-emitting laser can dissipate the bottom surface, that is, dissipate from the surface opposite to the laser light emission surface, so that different surface-emitting lasers are mounted in a single package as shown in FIG. In this case, the package structure becomes very simple and the cost can be reduced. Further, in the multi-wavelength integrated light source that is a laser module, heat radiation can be performed from the back surface of the package, and laser output can be extracted from the front surface of the package.

  As described above, in the fifth embodiment, the three surface emitting lasers 101, 102, 103 of red, green, and blue having the same configuration as the surface emitting laser described in any of the above embodiments are included in the package. Since the laser module is configured by mounting, a small integrated light source can be obtained, and as a result, an ultra-small laser irradiation apparatus can be realized.

  In the fifth embodiment, a multi-wavelength light source that outputs three wavelengths of laser light is shown as a laser module in which a surface emitting laser is mounted on a package. However, the multi-wavelength light source has two wavelengths. Even a thing with four or more wavelengths may be sufficient.

  Further, the number of surface emitting lasers constituting the laser module and the arrangement of the surface emitting lasers in the package are not limited to those of the fifth embodiment.

  FIGS. 9A and 9B are diagrams showing a modification of the number and arrangement of surface emitting lasers in the laser module of the fifth embodiment. FIG. 9A is a side view and FIG. 9B is a plan view.

  A laser module 150a shown in FIG. 9 realizes an RGB three-wavelength laser light source, similar to the laser module 150 shown in FIG.

  This laser module 150a is formed by mounting four surface emitting lasers on a package, and two green surface emitting lasers 106 and 107 are provided at the center of a package base member 151. It arrange | positions so that it may be located on an axis line. A red surface emitting laser 104 and a blue surface emitting laser 105 are arranged on another axis passing through the center of the package and perpendicular to the axis so as to sandwich the two green surface emitting lasers. Here, each of the surface emitting lasers has the same configuration as any of the surface emitting lasers of the first to fourth embodiments, and the arrangement of the four surface emitting lasers on the base member is relative to the center of the package. Are symmetrically arranged.

  The back surface of the base member 151 is a heat dissipation surface, and the lead terminals 104a, 105a, 106a, and 107a of the surface emitting lasers 104, 105, 106, and 107 are taken out from the back surface side of the base member 151. It is.

  In a laser module as an RGB light source that generates such red, green, and blue three-wavelength laser beams, the arrangement of the surface emitting lasers of the respective colors is important. That is, when an RGB light source is realized by a surface emitting laser, a green light source is particularly difficult to achieve high output. The green light source is usually realized by a ZnSe laser material, but its lifetime is reduced at high output. For this reason, it must be used at a relatively low output.

  Therefore, in the laser module 150 shown in FIG. 9, as shown in FIG. 9B, two green surface emitting lasers 104 and 105 are used and arranged close to each other, and the green surface emitting lasers of these green surface emitting lasers are arranged. A red surface emitting laser 106 and a blue surface emitting laser 107 are disposed on both sides. As a result, high output and long life of the laser light source can be realized.

  Further, the laser module 150 according to the fifth embodiment shown in FIG. 8 that is an RGB light source and the laser module 150a in which the number and arrangement of the surface emitting lasers in the laser module 150 are changed include a liquid crystal panel or a DLP (digital light Laser irradiation device that modulates the light emitted from the RGB light source with a two-dimensional spatial modulation element and projects the image by combining it with a two-dimensional spatial modulation element such as DMD (digital micromirror device) used in processing And can be applied to a laser display.

(Embodiment 6)
FIG. 10 is a diagram for explaining a semiconductor laser device according to a sixth embodiment of the present invention.

  The semiconductor laser device 160 includes a surface emitting laser that emits surface light from a laser beam, and a wavelength conversion element 161 that is disposed in a resonator of the surface emitting laser and converts the wavelength of the laser light from the surface emitting laser. Yes.

  Here, the surface emitting laser has the same configuration as the surface emitting laser 100a of the first embodiment. However, the surface emitting laser in this semiconductor laser device is not limited to the surface emitting laser of the first embodiment, and may be the surface emitting laser described in any of the second to fourth embodiments.

  The wavelength converting element 161 is made of a nonlinear optical crystal member disposed between the external mirror 1 constituting the resonator and the active layer 3 formed on the semiconductor substrate 2a.

Here, as the nonlinear optical crystal material, KTiOPO ₄ or polarization inversion MgOLiNbO ₃ is preferable. In particular, since the polarization inversion MgOLiNbO ₃ has a large nonlinear constant, the element length of the wavelength conversion element can be shortened, which is convenient for insertion into a resonator having a relatively short distance from the external mirror.

Next, the function and effect will be described.
The semiconductor laser device 160 according to the sixth embodiment can output laser light having a short wavelength by converting the wavelength of laser light generated by a surface emitting laser by the wavelength conversion element 161.

  Hereinafter, features of the semiconductor laser device 160 of the present embodiment will be briefly described.

  Since the wavelength conversion element generally has a narrow convertible wavelength tolerance, the wavelength of the fundamental wave that causes laser oscillation and the stability of the transverse mode greatly affect the wavelength conversion efficiency. In addition, in a normal surface emitting laser, when the single mode property of the transverse mode is deteriorated or changed, there is a problem that the conversion efficiency is greatly reduced or changed.

  In contrast, the semiconductor laser device of the sixth embodiment can achieve excellent stability and high efficiency.

  That is, since the nonlinear optical crystal member constituting the wavelength conversion element is arranged in the resonator, the power density of light incident on the nonlinear optical crystal member is increased, and high-efficiency conversion by the wavelength conversion element is possible. .

  In the sixth embodiment, the semiconductor laser device in which the surface emitting laser and the wavelength conversion element are combined has been shown in which the wavelength conversion element is disposed in the resonator of the surface emitting laser. You may arrange | position outside a resonator.

  FIG. 11 is a diagram showing a modified arrangement of wavelength conversion elements in the semiconductor laser device of the sixth embodiment.

  A semiconductor laser device 160a shown in FIG. 11 has a wavelength conversion element 161a arranged outside the resonator, and the other configuration is the same as that of the semiconductor laser 160 of the sixth embodiment.

  Further, the wavelength conversion element in the semiconductor laser device shown in FIGS. 10 and 11 may be a waveguide type element or a bulk type element.

  However, since the conversion efficiency in the wavelength conversion element largely depends on the condensing characteristic of the fundamental wave, it is important to use a single transverse mode. Therefore, the semiconductor laser device that outputs the short wavelength light by converting the wavelength of the output light of the surface emitting laser can control the transverse mode to a single mode as shown in the sixth embodiment, and has a high output. It is necessary to be able to perform wavelength conversion.

(Embodiment 7)
FIG. 12 is a schematic configuration diagram illustrating a laser projection apparatus according to the seventh embodiment of the present invention.

  The laser projection apparatus 170 according to the seventh embodiment includes a laser light source 171 and a projection optical system 172 that projects laser light emitted from the laser light source 171 onto a screen 173. And in the laser projection apparatus 170 of this Embodiment 7, the thing of the same structure as the surface emitting laser 100b of Embodiment 2 is used as a laser light source. However, the surface emitting laser used as the laser light source of the laser projection device 170 is not limited to that of the second embodiment, but may be those shown in other embodiments.

  Hereinafter, a laser display which is a kind of such a laser projection apparatus will be described.

  The laser display is composed of an RGB light source and a projection optical system, and projects a full-color image by projecting light from the laser light source onto a screen or the like by the projection optical system. As a projection method, it is classified into a type of projecting on a projection body such as an external screen or a wall and viewing the reflected light, and a type of irradiating light from the back of the screen as a rear projection type and viewing the reflected light. In either case, the color is recognized by the light scattered by the screen or the like.

  However, when a conventional laser display uses a semiconductor laser with high coherence, there is a problem in that speckle noise is generated due to interference of light scattered by the screen. As an effective method for reducing speckle noise, there is a method for reducing the coherence of laser light. In order to reduce the coherence of the laser light, it is effective to make the longitudinal mode multi-mode. In particular, the speckle noise can be greatly reduced by expanding the spectrum width of the longitudinal mode.

  In the surface emitting laser used as the laser light source of the laser projection apparatus of the seventh embodiment, as shown in the second embodiment, the spectrum is obtained by superimposing a high-frequency signal on a part of the plurality of divided electrode portions. The width can be increased and the coherence can be reduced. In order to reduce speckle noise, it is necessary to expand the longitudinal mode spectrum width in terms of wavelength to 1 nm or more, and more desirably to about 5 nm or more.

  Further, the longitudinal mode spectrum width can be further expanded by using a method of applying high-frequency signals having different frequencies to different electrode portions.

  The oscillation wavelength of the RGB light source is important from the relationship between the wavelength used for the laser display and the visibility. The wavelength used and the required light intensity are determined by the effect of visibility. The width of wavelength and color reproducibility is determined by the influence of chromaticity.

  FIG. 13 shows the relationship between the wavelength of the blue light source and the required output. Here, when the red wavelength is fixed at 640 nm and the green color is fixed at 532 nm, the relationship between the blue wavelength and the necessary output is shown to achieve a brightness of 1000 lm on the screen.

  The blue light has a sharp increase in required power because the visibility decreases when the wavelength is 430 nm or less. Further, when the wavelength is 460 nm or more, it approaches the green region, so that the color range that can be expressed becomes narrow and at the same time, the necessary power for expressing blue increases. At the same time, the red power increases.

  On the other hand, a blue surface emitting laser using a GaN semiconductor is usually a high output laser in the vicinity of 410 nm. In order to shift this wavelength to the longer wavelength side, it is necessary to increase the amount of In added. However, if the amount of In added is increased, the crystal composition deteriorates due to segregation of In, and the reliability and high output characteristics deteriorate. . Therefore, it is desirable to set the wavelength to 455 nm or less in a blue laser using GaN. From the viewpoint of color reproducibility, it is preferable to use a blue light source having a short wavelength because the range of colors that can be expressed in the blue region is widened.

  From the above viewpoint, the wavelength region of the blue surface emitting laser is preferably a region of 430 nm to 455 nm. More preferably, the wavelength region is desired to be 440 to 450 nm. In this case, it is possible to realize low power consumption and high color reproducibility by reducing required power.

  The red surface emitting laser can be realized by an AlGaAs semiconductor material or an AlGaInP semiconductor material. However, in order to achieve high output, it is preferable to set the wavelength region to a region of 630 to 650. Furthermore, the wavelength region is most preferably in the range of 640 nm ± 5 nm from the viewpoint of expanding visibility and the wavelength range of blue light used.

  The green surface emitting laser can be realized with a ZnSe-based semiconductor material.

  That is, in the Fabry-Perot semiconductor laser, the optical power density in the waveguide is high, and it is difficult to obtain reliability when using a ZnSe-based semiconductor material. However, when the green laser is configured as the surface emitting laser of the present invention, the optical power density in the crystal can be reduced, and high reliability can be ensured. As a wavelength region considering the color balance of the green surface emitting laser, a wavelength region of 510 to 550 nm is necessary. However, in consideration of the reliability of the surface emitting laser, the wavelength region is desirably a region of 510 to 520 nm, and high reliability and high output characteristics can be realized in this region. The green surface emitting laser can also be realized by a semiconductor material in which GaN is doped with a large amount of In. Even in this case, a wavelength region of 500 to 520 nm is desirable.

  As described above, the surface emitting laser according to the present invention can suppress hole burning caused by the optical power density distribution in the light emitting region, and can reduce deterioration of high output characteristics such as instability of the transverse mode and reduction of gain. It is useful as a light source for optical recording devices, optical display devices and the like that require high-power semiconductor lasers, and is also useful for other applications such as laser processing and medical use.

FIG. 1 is a diagram for explaining a surface emitting laser according to Embodiment 1 of the present invention. In the cross-sectional structure (FIG. (A)), the shape of a lower electrode (FIG. (B)), and the light emitting region of an active layer. 2 shows the light intensity distribution (FIG. 2C). FIG. 2 is a diagram showing another example of the shape of the lower electrode in the surface emitting laser of the first embodiment (FIGS. (A) and (b)). FIG. 3 is a view showing another example (FIGS. (A) and (b)) of the lower electrode structure in the surface emitting laser according to the first embodiment. FIG. 4 is a diagram for explaining a surface emitting laser according to the second embodiment of the present invention. In the sectional structure (FIG. (A)), the shape of the lower electrode (FIG. (B)), and the light emitting region of the active layer. 2 shows the light intensity distribution (FIG. 2C). FIG. 5 is a plan view (FIG. 5A) and a cross-sectional view (FIG. 5B) for explaining an application example of the surface emitting laser according to the second embodiment. FIG. 6 is a diagram for explaining a laser projection apparatus according to Embodiment 3 of the present invention. FIG. 7 is a view for explaining a surface emitting laser according to Embodiment 4 of the present invention. FIG. 8 is a side view (FIG. (A)) and a plan view (FIG. (B)) for explaining an example of a laser module according to Embodiment 5 of the present invention. FIG. 9 is a side view (FIG. (A)) and a plan view (FIG. (B)) for explaining a modification of the surface emitting laser according to the fifth embodiment. FIG. 10 is a diagram for explaining a semiconductor laser device according to a sixth embodiment of the present invention. FIG. 11 is a diagram for explaining a modification of the semiconductor laser device according to the sixth embodiment. FIG. 12 is a diagram showing the relationship between the wavelength and output required for the laser projection apparatus according to the seventh embodiment of the present invention. FIG. 13 is a diagram for explaining the output wavelength of the laser projection apparatus of the seventh embodiment, and shows the relationship between the blue light source wavelength and the required output. FIG. 14 is a diagram showing an example of a conventional surface emitting laser.

Explanation of symbols

1, 10, 21 External mirror 2, 2a, 22 Semiconductor substrate 3, 23 Active layer 4, 24 DBR layer 5, 25 Upper electrode 6, 6a, 6b, 26, 60, 600 Lower electrode 7a, 7b, 7c, 7d Fine Hole 8 Laser beam 9, 29 Recess 11 Insulating film 11a, 11b, 11c, 12a, 12b Hole 26a, 60a Inner electrode part 26b, 60b Outer electrode part 61 Resistance separating part 62 Insulating separating layer 62a Separating layer 100a, 100b, 100d, 200 Surface emitting laser 101, 106 Red surface emitting laser 101a, 102a, 103a, 104a, 105a, 106a, 107a Lead terminal 102, 104, 105 Green surface emitting laser 103, 107 Blue surface emitting laser 110 Semiconductor layer stack 120, 160 , 160a Semiconductor laser device 130, 170 Laser projection device 132 lens 133 spatial modulator 134 a projection lens 135,173 screen 150,150a laser module 151 based member 161,161a wavelength converting element 172 projecting optical system

Claims (25)

A surface emitting laser that performs surface emission of laser light,
An active layer formed on a semiconductor substrate;
A pair of electrodes for injecting carriers into the active layer;
One of the pair of electrodes is composed of one electrode layer, and current is injected from the one electrode into the active layer at different current densities in the central portion and the peripheral portion of the one electrode. Is,
A surface emitting laser characterized by the above. The surface emitting laser according to claim 1, wherein
A semiconductor layer stack including the active layer, wherein a plurality of semiconductor layers are stacked on the semiconductor substrate;
The surface density at which the electrode layer and the semiconductor layer laminate are in contact with each other is different between a central portion of the electrode layer and a peripheral portion thereof.
A surface emitting laser characterized by the above. The surface emitting laser according to claim 1, wherein
The one electrode is formed by forming a plurality of micro holes in the electrode layer constituting the electrode so that the occupation density of the micro holes is different between the central portion of the one electrode and the peripheral portion thereof.
A surface emitting laser characterized by the above. The surface emitting laser according to claim 1, wherein
In the one electrode, the resistance value of the electrode layer constituting the electrode is different between the central portion of the one electrode and the peripheral portion thereof.
A surface emitting laser characterized by the above. The surface emitting laser according to claim 1, wherein
A semiconductor layer stack including the active layer, wherein a plurality of semiconductor layers are stacked on the semiconductor substrate;
Having a resistance layer formed between the semiconductor layer stack and an electrode layer constituting the one electrode;
The resistance value of the resistance layer is different between a portion corresponding to the central portion of the one electrode and a portion corresponding to the peripheral portion thereof.
A surface emitting laser characterized by the above. The surface emitting laser according to claim 1, wherein
A semiconductor layer stack including the active layer, wherein a plurality of semiconductor layers are stacked on the semiconductor substrate;
A resonator that amplifies the light generated in the active layer so that laser oscillation is generated includes a reflection layer included in the semiconductor layer stack, and an external portion disposed away from the semiconductor layer stack so as to face the reflection layer Consisting of a mirror,
A surface emitting laser characterized by the above. The surface emitting laser according to claim 6, wherein
The external mirror is a partially transmissive mirror having concave surfaces on both sides.
A surface emitting laser characterized by the above. The surface emitting laser according to claim 1, wherein
A semiconductor layer stack including the active layer, wherein a plurality of semiconductor layers are stacked on the semiconductor substrate;
The semiconductor layer stack includes a supersaturated absorber that is disposed in the vicinity of the active layer and absorbs supersaturated carriers in the active layer.
A surface emitting laser characterized by the above. The surface emitting laser according to claim 1, wherein
The oscillation wavelength of the surface-emitting laser light is a wavelength within a range of 430 to 455 nm.
A surface emitting laser characterized by the above. The surface emitting laser according to claim 1, wherein
The oscillation wavelength of the surface-emitting laser light is a wavelength in the range of 630 to 650 nm.
A surface emitting laser characterized by the above. The surface emitting laser according to claim 1, wherein
The oscillation wavelength of the surface-emitting laser light is a wavelength within a range of 510 to 550 nm.
A surface emitting laser characterized by the above. The surface emitting laser according to claim 6, wherein
A non-linear optical material that is disposed between the external mirror and the active layer and converts the wavelength of laser light;
A surface emitting laser characterized by the above. The surface emitting laser according to claim 1, wherein
A semiconductor layer stack including the active layer formed by stacking a plurality of semiconductor layers on the surface of the semiconductor substrate;
The semiconductor substrate is formed by etching a part of the back surface to the vicinity of the surface of the active layer to form a recess.
A surface emitting laser characterized by the above. A semiconductor laser device comprising: a semiconductor laser that outputs laser light; and a wavelength conversion element that converts the wavelength of the laser light from the semiconductor laser,
The semiconductor laser is a surface emitting laser according to claim 1,
A semiconductor laser device. A laser module in which a plurality of semiconductor lasers are integrated in one package,
Each of the semiconductor lasers is a surface emitting laser according to claim 1,
A laser module characterized by that. The laser module according to claim 15, wherein
The plurality of semiconductor lasers are arranged such that each semiconductor laser is positioned at the apex of a regular polygon whose center coincides with the center of the package.
A laser module characterized by that. A laser projection apparatus comprising: a semiconductor laser that outputs laser light; and a projection optical system that projects the laser light output from the semiconductor laser,
The semiconductor laser is a surface emitting laser according to claim 1,
A laser projection apparatus characterized by that. The laser projection device according to claim 17, wherein
The surface emitting laser emits laser light whose longitudinal mode spectrum is multimode,
A laser projection apparatus characterized by that. The laser projection device according to claim 17, wherein
The surface emitting laser emits laser light having a substantial width of a longitudinal mode spectrum that is spread by 1 nm or more.
A laser projection apparatus characterized by that. A surface emitting laser that performs surface emission of laser light,
An active layer formed on a semiconductor substrate;
A pair of electrodes for injecting carriers into the active layer;
One of the pair of electrodes is divided into a plurality of electrode portions,
A laser driving voltage on which a high frequency component is superimposed is applied to at least one of the plurality of electrode portions.
A surface emitting laser characterized by the above. The surface emitting laser according to claim 20,
The plurality of divided electrode portions are arranged substantially uniformly around the emission center of the laser beam,
A surface emitting laser characterized by the above. The surface emitting laser according to claim 20,
Injecting current from each of the electrode portions into the active layer so that the current density is higher in a region closer to the emission center of the active layer,
A surface emitting laser characterized by the above. The surface emitting laser according to claim 20,
Applying a modulated laser driving voltage to at least one of the plurality of electrode portions;
A surface emitting laser characterized by the above. The surface emitting laser according to claim 20,
Driving each semiconductor laser part formed by each electrode part with a different injection current;
A surface emitting laser characterized by the above. The surface emitting laser according to claim 20,
A semiconductor layer stack including the active layer formed by stacking a plurality of semiconductor layers on the surface of the semiconductor substrate;
The semiconductor substrate is formed by etching a part of the back surface to the vicinity of the surface of the active layer to form a recess.
A surface emitting laser characterized by the above.

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